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of 61Weld-FAQ: Useful Answers to Common Questions

5/11/2011http://www.welding-advisers.com/Weld-FAQ.html

Weld-FAQs

Mig or Stick? Alternatives to Welding Welding thin to thick Sections Double V-Groove welding of thick Pipe EBW Repair of a rejected Casting Weld Repair of Aluminum Castings Weld Crack Repair Keeping Flux in Place Out of Position Welding Parameters for Welding 1/2 inch plates Welding a Shaft Spatter Reduction in FCAW Welding Stainless Steel Welding Stainless Handrails Welding Stainless to Nickel Alloy 600 Stainless to Mild Steel Welding Brazing Carbon Steel to Stainless Stainless to Cast Iron Welding Cast Iron to Mild Steel Welding Repairing a Crack in Cast Iron Welding of AISI 1141 Welding of 1018 to 4140 Welding a splined end onto a hard AISI 4140 Shaft Welding of AISI 440C Again on Welding AISI 440C Weld repair of nitrided tools Process Comparison Carburize with Oxyacetylene Flame? Fillet welding of Rimmed Steels Manufacturing a Spherical Vessel Use of Low Hydrogen Electrodes Strength of Stainless Steel Spot Welds Sorting unweldable Stainless Steel Welding thin Stainless Steel Sheets Stainless Steel Tanks for Water Repairing Holes in Aluminum Panels Welding of Brass Sheets Welding Leaded Brass Welding Aluminum Bronze to Mild Steel Joining Copper to Steel Welding Copper to Stainless Welding Copper to Stainless (B) Welding Copper to Stainless (C) Welding Copper to Aluminum GMAW with straight CO2 gas

Brazing Fittings Furnace Brazing of Tubular Joints Brazing in Steps Leak Test Class A Welding Hardening Heavy Sections Furnace Hardening of Steels Heat Treating Tool Steel in a Bag Normalizing welded Mild Steel Grinding a Plate and its Distortion Preventing Distortion Straightening a Warped Beam



Spot Welding Dissimilar Materials Projection Welding of Steel Nuts Welding together Different Carbon Steels Welding Aluminum to Stainless Welding Steel to Aluminum Welding Titanium to Stainless Welding Titanium Clad Steel Welding Titanium to Cobalt base Alloy Gas Metal Arc Welding Titanium Welding Tin to Stainless Steel Snapping Sounds from the Roof Welding in cold Weather Semi Automatic Ultrasonic Inspection Thickness Range of a Plasma Cutter Oxyfuel Gas Bevel Cutting Welding Effects on Aluminum Structures Welding with Robots Cut Pie Welding Fumes from welding zinc coated steel Welder Qualification Threaded Hole Repair Attach Nut to Zinc Hub Designing a Hinge Welding High Tensile Bolts Cutting Pipes and MPI Joining Hybrix Tungsten for Titanium Tig Welding Lead Brazing Flux Removal Selecting Carbide for Hardfacing Braze-Welding of Steel Inside Tube Inspection Safety in Hydrogen Furnaces Disposing of Arc Strikes Change of Material Proper Water Cooling of Spot Welding Electrodes Increasing the Weld Deposition Rate Find if an aluminum alloy is weldable or not Welding Unknown Materials Hard Facing of Austenitic Manganese Steel Stress Relieving Test

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Mig or Stick? [From PWL#070, Section 3]

Q - I am a welder that welds with a lot of different processes. My question is this. We are welding up a fabrication table to build a container box that will weigh 50,000 lbs.

I was told that it should be SMAW welded with E-7018 and not to weld it with Mig. The mig wire we use is ER-70. What is the difference in the two processes? Aren't both electrodes classified as being good for 70,000 psi? Should I make this structural weld with the Mig or Stick?

A - Thank you for your question.

I feel from it that you are a good, experienced and conscientious welder. I am sure you will obtain good welds with both processes. Keep up the good work as you please and it will be OK. [It is true that inadequately skilled welders may produce low quality welds with any process.]

One of the disadvantages attributed to Mig (GMAW) when performed outdoors is the possible loss of shielding gas due to the wind: this is possibly the concern of those who "told" you to avoid Mig. It depends upon the circumstances, if suitable wind shields can or cannot be set up.

It is accepted that self shielded Flux Cored Arc Welding (FCAW) is less prone to the loss of shielding atmosphere while providing the continuous electrode advantage as Mig does. However breathing FCAW fumes is more dangerous to the welder's health. And of course slag has to be removed between passes and at the end of the process.

As far as strength and stability are concerned the design has to be adequate but there are no differences between the two processes that should bother you as long as sound welds are produced.

There may be quite a remarkable difference in the cost of welding though, but this is up to the management to decide and be responsible for.

What bothers me is that you are made to work in a vacuum of responsibility.

About a year ago I wrote an article titled "Where is the Welding Management?" that you can find at http://www.thefabricator.com/article/TECHCELL/where-is-the-welding-managementr

As long as your work is good, you will grudgingly get moderate praise (Not too much, lest you may think you are worth a pay raise). But should one of your construction collapse or get damaged you will get all of the blame and of the consequences.

your Welding Problems?

Click on Welding Consultation.



If at all possible, you should request from your management precise, written instructions in the form of clear, signed Drawings and Welding Procedure Specifications (WPS).

You are not supposed to be "told" anything, you should get only written instructions. Those who give you welding work must take full responsibility in writing for whatever you are requested to perform at the best of your ability, but not any more than that, including process selection.

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Alternatives to Welding

Q: When and why should Alternatives to Welding be considered?

A: Whenever Welding is difficult and expensive and if there is no essential need for the kind of metal continuity provided by welded joints. The main point is that welding processes in general are associated with elevated temperatures.

In many situations the application of heat may have adverse effects like crack formation, hardness and strength changes, production of brittle phases, microstructural modifications affecting corrosion resistance properties, unacceptable deformations, alignment and fit problems, introduction of residual stresses.

If the risks following the above effects entail the adoption of special procedures to counteract them, then welding becomes a much less attractive solution.

Among possible alternatives one could consider the following. Brazing and Soldering that require less heat and may provide adequate properties to the joint. Otherwise Mechanical Fastening, structural Adhesive Bonding, surface modification if effective, elimination of joint by design change.

Welding thin to thick Sections

Q: A thin tube has to be welded to a thick plate or bar: why is it so difficult to do so?

A: The thick element absorbs a large quantity of heat before reaching melting temperature. On the contrary the thin tube melts almost immediately. Therefore to weld properly one has to change the configuration of the joint so that the difference in thickness be kept to a minimum.

The bar or plate has to be machined so that at the joint location the thickness be comparable to that of the tube, or an intermediate transition element of proper shape and size must bewelded between the two elements. Alternatively, if the joint shape permits it, one should consider brazing or friction welding.

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Double V-Groove welding of thick Pipe

Q: A double-V-groove joint in a thick Pipe requires welding both from inside andfrom outside. Is there a preference as to which side to weld first?

A: Yes, definitely. As the pipe is thick, the process used will most probably beeither Gas Metal Arc Welding or Submerged Arc Welding which are both providinghigh weld deposition rate.



In order to guarantee the highest quality the rootpass, however being done, has to be back gouged, that is ground for all itslength until sound metal is found. This grinding operation with a portablegrinder can best be performed unhindered from the outside. Therefore the rootpass has to be laid down first from the inside of the pipe.

Additional tips:please note that, for longitudinal welds, run out tabs have to be provided at both ends. Furthermore thefirst weld (from the inside as explained) will start at one end for a length ofabout 150 mm (6 inches) only. This short weld will prevent distortion andoverlapping of the edges under the shrinkage strains caused by the long weld.

Then its inner end has to be ground clean to permit perfect blending with theupcoming weld that will start at the other end of the pipe and proceed towardsthe already welded short stretch. Once the root weld is completed and backgougedthe filler passes will be performed as convenient.

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EBW Repair of a rejected Casting

Q: An expensive finish machined cast aluminum housing was rejected because aninternal bore, located deep inside the part, at a great distance below the faceof the top flange, was found oversize. How could it be salvaged by repairwelding?

A: Regular welding would not be an acceptable solution. But Electron BeamWelding a spare bushing in place, although expensive, may salvage the costalready invested in the finished and rejected part.

By welding in place a spare sleeve the process has the potential:

of precisely focusing the beam on top of the joint, despite the distance, of introducing the least amount of heat, avoiding damage to

mechanicalproperties and preventing unacceptable distortion, of producing a thin and deep, precisely located weld seam, of avoiding the need for repeated heat treatment, of permitting thorough non destructive testing to qualify the repair, of being performed within the shortest turnaround time limiting the delay

indelivering a replacement part.

(Note: The above is presented as Example 480 on page 541 of Metals Handbook Vol.6, 8th Edition).

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Weld Repair of Aluminum Castings [from PWL#042, Section 3]

Q: How are Aluminum Castings repaired?

A: Aluminum Alloy castings scrapped in the foundry because of surface defects and lack of dimensional integrity can be salvaged by welding except if they present massive porosity.

Gas tungsten arc welding (GTAW) with high frequency stabilized Alternating Current is normally used to repair sound castings. Inclusions should be prevented by taking care to avoid touching the surface with the pure tungsten electrode.



Argon with or without helium can be used as a shield. Helium helps generating a hotter arc if necessary. To prepare for welding one should remove defects, especially cracks, by dry chipping with a rounded tool or by hand milling, to obtain a smooth area. One should never attempt to weld on the original casting external rough surface without first removing the oxidized layer.

Removal of oil and grease is performed using vapor degreasing or clean solvents.Use of acid etch is not recommended. If impregnation was applied, it should be removed before welding. A clean stainless steel wire brush should be used to remove thick oxide layers just before welding.

Filler material alloy is usually the same as that of the casting. Preheating is needed only in exceptional cases to overcome difficulties.

On suitably prepared surfaces of sound castings, with oxide layers thoroughly removed, one should be able to weld as easily as on wrought alloys. It would be good practice to look for cracks in the weld by using penetrant inspection. Radiographic inspection may be required by contract in certain cases.

If the original castings are to be heat treated, also the repaired ones should follow the same process. Weld repairing of heat treated casting would impair their mechanical properties.

The feasibility of repair of aluminum alloy castings that were already heat treated and machined is questionable because of stresses and deformations likely to develop during welding.

An example of such a repair performed by developing a special procedure with electron beam welding is reported in this page here above under the title "EBW Repair of a rejected Casting".

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Weld Crack Repair in a Transition Part [From PWL#050, Section 3.]

Q: Al 5356 vs SS 304: would you help me to find the proper filler metal for welding together these two materials?

A: The answer to this question is straightforward: Unfortunately the two materials are incompatible, that is they cannot be fusion welded together. Depending on configuration and requirements they might be welded by solid state processes (like friction welding).

Please see my article: Joining Incompatible Materials http://www.thefabricator.com/ArcWelding/ArcWelding_Article.cfm?ID=1590 and also my article (7) Welding Incompatible Material Combinations in PWL No. 043 for March 2007 at http://www.welding-advisers.com/PRACTICAL_WELDING_LETTER-PracticalWeldingLetterNo43.html

But it appears that the question was not formulated correctly. The new question was now as follows:

Correct Q: "This is a photo of the joint we are talking about. The equipment is a (liquid) nitrogen tank carrier. I need to repair the cracked weld. Would the reduction



pipe be a transition material between Aluminum and Stainless?"

A: Yes. The reduction pipe is a transition part obtained made by friction welding together an aluminum and a stainless elements. The aluminum side of the transition element was later arc welded to the aluminum construction, while the stainless part was welded to the stainless tube.

As the crack appears to be wholly confined to the aluminum joint, it should be dealt with like a repair in an aluminum part.

Conclusion: A misleading question may produce a useless answer.

Cracked Weld in a Reduction Tube The Question Mark points at the location of the Friction Welded Joint of the Transition Part, connecting an aluminum element to a stainless cone.

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Keeping Flux in Place

Q: How can one keep Submerged Arc Welding Flux in place underneath a joint?

A: While performing Submerged Arc Welding of a groove joint from above, in flatposition, backing flux is needed also at the underside. To keep it in contactwith the surface and to avoid contamination, one can press the flux against theback of the joint by the use of an air inflated hose laying at the bottom of ametal channel full of flux, on top of which the joint is placed.

By this methodthe underside of the root pass remains clean and sound so that little grindingis needed before depositing the next bead from the opposite side of the joint.

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Out of Position Welding [from PWL#039, Section 3]

Q: What makes an all position welding rod/wire, 'all position'? What is the difference between this type of rod and the others for flat or horizontal only?



A: Covered electrodes (SMAW) for flat and horizontal positions are optimized for maximum weld deposition rate. As such they provide a large but still manageable weld pool that does not run out.

Out of position electrodes, useful for vertical or overhead welds, are made with modified shielding cover, designed to control the viscosity of the molten metal to make it more sluggish and capable of adhering to the surface even in overhead position, instead of dripping down immediately.

The electrode cover for these electrodes contains elements that affect the wetting of the base metal and the viscosity of the molten weld metal. Viscosity can be controlled also, within limits, by mastering the technique and by adjusting the current. Adequate skill is essential to obtain good and repeatable results.

Note that vertical and overhead joints are welded with smaller diameter electrodes than would be used in flat position for the same thickness, with corresponding lower deposition rates.

It should be noted that the welding position is an important variable that can affect the weld metal quality. For this reason one should select, whenever possible, the flat position.

See also Vertical Welding Tips.

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Parameters for Welding 1/2 inch plates [From PWL#051, section 3]

Q: I've been set a task to find the welding parameters for welding two mild steel plates together using Manual Metal Arc Welding [...] The plates are 12.7 mm or 1/2 inch in thickness. I need to find parameters for edge preparation, welding current, welding speed, AC/DC Current and electrode type/size.

A: We will assume that the plates are to be welded in the flat position, edge to edge with groove joint. The given thickness cannot be welded in a single pass with the process specified, so that the edges are to be machined by selecting one of the two most common configurations.

We will refer to the recommendations of a document readily available online, Welding Joint Identification and Types of Welds from http://aged.calpoly.edu/AgEd410/Presentations/Welding%20Descriptions.ppt although other valid documents can be found in any technical library.

In page 5 of that presentation, beveled butt joints are described:

3/8 to ½ inch metal can be welded using a single V or U joint. ½ inch metal and up can be welded using a double V or U joint.

The bevel dimensions and the gap can be as in the illustration given there.

The joint proposed above is therefore on the high limit of single V joint or on the low limit of the double V joint. U joints will not be considered in this case.

What is the difference?



Single V joint is welded from one side only. For plates it may make not much of a difference. For a tube or vessel, especially if of limited dimensions, the internal side may not be easily reachable for welding.

Double V joint requires more expensive machining, possibly including a new positioning and set-up in the milling machine used. If a flame or plasma machine is available, bevels could be also cut with this equipment.

It requires much less weld metal though, about half of it, for purely geometrical consideration. This has remarkable consequences, much less heat input is required and less deformations are generated. For welding from both faces the construction has to be turned upside down (if positioned flat), which may be an expensive exercise for bulky and heavy constructions.

The electrode to be used, if special requirements are not imposed, can be E-6011 per AWS classification, that is suitable for AC. The power source for AC is a simple transformer, a quite economic piece of equipment. If other electrodes were selected, welded by DC with more expensive equipment, then Arc Blow (deflection of the arc due to magnetic forces) could become an issue.

First, with the plates securely clamped to the weld table, tack welding should be performed. This means short stretches of weld bead, about 13 mm (1/2") long, at some distance from each other, say 100 to 150 mm (4 to 6"). These should be deposited in proper sequence, at distant places to avoid localized shrink stresses.

Then tack welds should be cleaned from slag and ground to permit smooth blending of the coming new weld beads.

Electrode size depends on operator's skill and preference.It could be 3/32" (2.4 mm) at the manufacturer's recommended current, about 60-80 Amp or 1/8" (3.2 mm) at about 80-100 Amp.

The root pass could be performed with backing, if advisable, that should normally be removed after welding. For best quality the root pass should be gouged from the back side and a new pass should be added.

Slag of each pass has to be thoroughly removed before applying subsequent passes.

Welding speed is strongly operator dependent and should be measured. A more useful parameter is probably the weld deposition rate in weight units per hour.

The total number of passes needed to fill the groove depends on the operator technique, if depositing thin parallel beads, or wide beads obtained by weaving the electrode from side to side. Larger size electrodes could be used but at the risk of higher heat input and increased deformation.

Three types of deformation should be foreseen and prevented. See the page on Welding Distortion.

The first deformation to be prevented is the overlapping of the joint ends as shrinkage tends to close the gap. As mentioned elsewhere, the first weld will start at one end of the joint for a length of about 150 mm (6 inches) only. Then the upcoming weld will start at the other end of the joint and proceed towards the already welded short stretch.

The second type of deformation affects the single V groove joint. As the weld metal in the groove shrinks upon cooling it tends to pull in a direction transversal to the joint. The two plates lying flat tend to decrease the angle between them (from 1800



to 170 - 1600 and even less). Imagine a book lying open and flat, slowly starting to close.

To prevent this movement one should increase the angle even more before welding, laying the plates not flat but like a roof (say at 2000). With the correct starting angle, welding is going to straighten the plates flat. The double V groove joint will be much less sensitive to this deformation, especially if welding proceeds alternatively from both sides.

The third is the longitudinal shrink along the joint which may cause the joint to curve following an arch. This can be minimized by welding short stretches at a time in a proper sequence, that will avoid excessive localized heating, and by peening with a hammer the weld bead while still hot, to introduce compressive stresses to counter the shrinking stresses.

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Welding a Shaft [From PWL#052, Section 3]

Q: - I am trying to create a special longer input shaft for car manual 5 speed transmission by welding a newly created, heat treated SAE8620 shaft (HRC58-62) to the gear end section made from heat treated SAE4620 (HRC58-62). Shaft end is SAE 8620 HRC 58-62, (carburized) .025-.035" case depth, quenched in hot oil @ 350F and tempered @300F for one hour.Gear end is SAE 4620 HRC 58-62 with same heat treatment as shaft end. The parts are assembled with light press fit and welded.

Samples have been preheated to 300F and TIG welded with 80SD2 filler metal, air cooled with no PWHT (Post Weld Heat Treatment).

Using GTAW setup, I need recommendation for pre-weld heating, filler material, and post-weld cooling process. Must be careful not to create cracks or weak areas at weld and must not anneal weldment so as to reduce hardness of gear teeth. Is there a post weld non-destructive quality inspection process?

I am modifying existing already hardened input shafts (gear end piece) by welding on new longer shaft end with different spline (26T vs 10T original). I had the shaft end hardened as needed for wear resistance for the clutch to slide along the splined area.

A: - Hardness of the two elements is way too high to be suitable for welding. Welding is here a recipe for trouble.

If you were to cut a sample part through the welds already done and run a microhardness survey you would find that the surroundings of the weld have been annealed or softened, while the Heat Affected Zone bordering the welds has hard, untempered martensite, which is dangerous in that it can develop cracks if subject to fatigue. This combination of microstructures is not recommended in a stressed part.

In principle it is not good design practice.

A non destructive testing could be found, but the proposed welding should not be approved for such a critical application.

If you could first weld annealed materials and then carburize, harden, temper AND



control Heat Treatment deformations, you might be able to produce a sound part.

[Note: There may be an acceptable way out though, if the project is important enough to warrant paying for consultation]

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Spatter Reduction in FCAW [From PWL#047, Section 3]

Q: How can spatter be reduced in Flux Cored Arc Welding?

A: For a general overview of this process see our website page on Flux Cored Arc Welding Tips and other pages referenced thereby.

FCAW is often perceived as a low cost process, even for Hobby and Home work, in that shielding gas is not required (flux cored wire is self shielded), thus reducing equipment cost and simplifying procurement of consumables.

For industrial applications shielding gas (for steel mostly Argon with 8-25 %CO2) is almost always employed, with remarkable influence of the gas mix on the arc and on the resulting welds.

It is also claimed to be easier to master than Gas Metal Arc Welding (GMAW), in that only basic skills are required to obtain acceptable welds in all positions. Penetration and deposition rate are higher than for Shielded Metal Arc Welding.

The often cited additional advantage is that flux cored filler material, by virtue of special ingredients in the flux can be more tolerant to the presence of rust or mill scale on the steel.

The production of thicker smoke and fumes is considered an advantage when welding outdoors because an occasional light breeze would not remove the shielding effect around the weld. It can be a nuisance and a health risk if welding indoors, unless fume extraction is in place to protect the welder.

Slag has to be removed in any case after welding and before any additional weld is done on top of the deposited weld beads.

When using traditional constant voltage power supplies the polarity selected is mostly DCEP (Direct Current Electrode Positive) that gives a stable arc, low spatter (at the correct voltage), a good weld bead profile and optimum penetration

It is important to know which metal transfer mode is used. At lower currents the short circuit transfer mode is operating, usually when welding steel less than 3 mm (1/8") thick.

Spatter is best controlled by using voltage adjustment to obtain a crisp, consistent crackle sound. One should learn from practice to recognize the correct sound associated with short circuit welding.

As an indication, the starting voltage for short circuit applications with flux cored wire of size 0.8 - 1.0 - 1.2 mm(0.030 - 0.035 - 0.045") is 16 to 18 V.

The corresponding wire feed speed could be 1.8 to 10.7 m/min (70 to 420 inch per minute), that would provide 50 to 170 Amps, 65 to 200 Amps, and 130 to 220 Amps for the three wire sizes.



If the crackle of the weld consists in a soft plop sound with some spatter, reduce voltage one volt at a time until the correct sound is generated and spatter is eliminated.

If on the contrary the sound is harsh and explosive with no soft sounds, then increase one volt at a time until spatter is substantially reduced.

With higher current levels the metal transfer becomes the spray mode. Here the arc length should be kept minimal and again one should strive to obtain the consistent crackling sound already described.

Voltage for spray mode would preferably be between 24 and 34 V, a good starting point would be 30V.

For 1.0 mm (0.035") wire size the wire feed speed could be between 10.7 and 14.2 m/min (420 and 560 ipm) that would provide 215 to 300 Amps for a normal stickout (electrode extension) between 13 to 16 mm (1/2 to 3/4").

For 1.2 mm (0.045") wire size, the wire feed speed could be between 8.9 and 16 m/min (350 and 630 ipm) that would provide between 250 to 360 Amps. Voltage adjustment in spray mode goes in opposite direction relative to short circuit mode.

Decreasing voltage (one volt at a time) shortens the arc, but too low a value will bring the electrode to plunge in the weld pool with consequent spatter. Then the voltage should be increased again until the optimum is reached and spatter is substantially reduced.

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Joining Copper to Steel [From PWL#049, Section 3]

Q: - We need to TIG weld 3/8" ODx.035" wall copper (SB-75) tubes to a carbon steel tube sheet. We will use Argon gas for shielding, 2% Thoriated Tungsten, would you recommend a low silver (5%) or a high silver (15%) filler metal or something altogether different. Would this be a Brazing (SB) or would this be a Tig (GTAW) process.

A: - Joints designed for welding have a shape different from those suitable for brazing. The selection is based upon the function of the assembly in service and on the ease of joining, strongly dependent upon the facilities available and on production quantities, which influence production costs.

Please note that ASME SB-75 includes the following materials:

ASME SB-75

Copper UNS No. Type of Copper

C10100 Oxygen-free electronic

C10200 Oxygen-free without residual deoxidants

C10300 Oxygen-free, extra low phosphorus

C10800 Oxygen-free, low phosphorus

C12000 Phosphorus deoxidized, low residual phosphorus

C12200 Phosphorus deoxidized, high residual phosphorus



If the joint design specifies butt welding of tube ends, one can Tig weld the tubes with Filler Metal: ERCuAl-A2 or ERCu or ERCuNi-3 The arc is directed at the more conductive metal (copper).

If the tubes enter into the tube sheet for a suitable overlapping length, depending on service requirements, with clearance on the diameter of about 0.05-0.13 mm (0.002-005") at brazing temperature, one can select a silver based filler metal and a corresponding flux from quite a large list of available materials. For low production quantities an oxyacetylene flame would be adequate. For mass production furnace brazing in a controlled atmosphere would be probably more economic. Cleanliness is always of the utmost importance.

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Welding Leaded Brass [From PWL#053].

Q: We are welding a cylindrical brass part (60Cu+37Zn+3Pb with approximatively 2% impurities) with stainless steel pipe, by oxyacetylene flame. The Brass part section is 3.5 mm thick where it is being welded and the rest of the part is 8.5 mm thick.Some of the pieces are breaking on the 3.5 mm thickness side. Can you explain what is the reason?

A: The stainless steel pipe should be of the weldable type, not prone to sensitization, otherwise it could become easily corroded. See our page on Stainless Steel Welding.

The filler metal and the flux used were not specified but this is not the main thing.

However the fusion process selected is not suitable for the application, because lead (Pb), added for improving machinability, causes the brass to become hot-crack susceptible upon welding. Therefore this alloy should not be fusion welded.

If arrangements can be made to produce overlapping joints with small clearance, brazing could be performed instead of welding, with silver base alloys. See our page on Brazing.

Otherwise substitution of the said copper alloy with unleaded brass should be considered.

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Welding Stainless Steel

Q: What shall I use to weld stainless steel?

A: This question, which I actually received from a reader, is unfortunately not sufficiently defined: therefore it is not possible to give a meaningful answer. One must first describe a few parameters to qualify the solution requested.

Material: as explained in another page on Stainless Steel Welding (opens a new page), there are many different types of steels loosely responding to this category, but they can be grouped in four or five families having important characteristics in common.



Each family/type has to be addressed separately as they behave differently during welding and need specific instructions.

Therefore, before tackling a job, one has to know positively or to have analyzed qualitatively the stainless steel type involved, for identifying at least its family.

Joint: type and dimensions of the needed joint must be stated. One should pay attention to the deformations that may develop as a consequence of welding and take proper precautions.

Process: If we think of a small shop and of an occasional job coming up once in a while, we will try to adapt whatever process is available that will give an acceptable solution. If we have a larger shop with plenty of equipment to choose from, and with experienced workforce with the needed skills, we will be able to select in complete freedom. If we are planning for mass production we will be able to purchase the equipment capable of the most cost effective welding.

Consumables need to be suitable both for base material and for process selected.

Of the common processes that can be used to weld stainless steels we will consider only three:

the Shielded Metal Arc Welding (SMAW) or Manual Metal Arc (MMA) with covered electrodes, see Shielded Metal Arc Welding Tips (Opens a new page).This manual process is the first to think of, if the material is not extremely thin. By using multiple passes one can weld substantial thickness.

the Gas Tungsten Arc Welding (GTAW or Tig) with nonconsumable tungsten electrode, see Tig Welding Tips (Opens a new page).This manual or mechanized process can produce very clean welds, as needed for food or pharmaceutical industries. It is not used, generally, for thick materials except for the first pass.

the Gas Metal Arc Welding (GMAW or Mig) with consumable electrode, see Mig Welding Tips (Opens a new page).This process provides higher deposition rate than the two above, and is best used for industrial applications on substantial thickness or over a root pass made by GTAW or GMAW. Can be used for Robotic Arc Welding (Opens a new page).

One should note that the old time Oxyacetylene Gas welding process, requiring the use of fluxes for removing the oxidized layer, should not be considered for quality welds.

Filler metals for stainless steels are briefly introduced in an article in Practical Welding Letter No.02 for October 2003, visible by clicking on PWL#002.

Standards for stainless filler metals are listed in the page on Stainless Steel Welding indicated above.

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Welding Stainless Handrails [from PWL#074]

Q - I had a contractor install handrails on the stairway. I wanted stainless steel which he used however at the "welded joints" we are seeing what looks like corrosion. If he did use stainless filler rods why would we see corrosion?



How can we fix this corrosion with a paint or chemical?

A - Assuming that your contractor installed austenitic stainless steel type 302 or 304 handrails, and assuming that the filler rods were correct (should have been type 308L or 347), there is nonetheless the question of sensitization as explained in my page http://www.welding-advisers.com/Welding-stainless.html

It appears that the contractor either did not know or did not care. He should have looked for base material type 304L or 321 to avoid the corrosion problem in the first place, with the above filler material.

If the corrosion is concentrated at the joints, to mask it you may possibly paint with aluminum pigments paint, but you may need to repeat painting frequently.

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Welding Stainless to Nickel Alloy 600 [From PWL#081]

Some recent queries asked for information on welding stainless to nickel. As the queries did not specify the request in more detail, given the rich variety of stainless steels and also the different types of nickel base alloys available, this note will refer to austenitic stainless steels and to nickel base alloy 600.

The following indications may provide some orientation but one should keep in mind the service conditions and check if the proposed filler metal selection is suitable to the applications considered.

You may wish to see also our page on Welding Nickel that includes two tables of Filler Metal chemical compositions, and also a short note on Filler Metals for Welding Nickel published (4) in the Practical Welding Letter PWL#062.

For the dissimilar welding of austenitic stainless steel to nickel alloy 600 the following filler metals are recommended.

Welding Electrodes per AWS A5.11: ENiCrFe-2, ENiCrMo-3, ENiCrCoMo-1, ENiCrFe-3

Welding bare rods per AWS A5.14: ERNiCr-3, ERNiCrFe-7, ERNiCrMo-3

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Stainless to Mild Steel Welding

Q: Is it possible to Arc weld Stainless Steel to Mild Steel?

A: Yes, Austenitic Stainless Steel is currently welded to Mild Steel, with certain precautions.

First, the Stainless should be of a composition not susceptible to sensitization otherwise its corrosion resistance properties will result impaired by welding. (See on this problem the article in the Welding Advisers Site, Click on Welding Stainless Steels .)

Second, especially if the mild steel element is thick, it is customary to weld on top of



it a layer of stainless (Type 309 or type 312) or of high nickel filler metal: this procedure is called buttering. The final welding thus occurs between two stainless surfaces.

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Brazing Carbon Steel to Stainless [From PWL#069, Section 7].

Q: How one brazes carbon steel to stainless steel?

A: There are different considerations and precautions that have to be taken into account, depending on actual configuration and joint details. Also production quantities will dictate the most economic assembly and heating methods.

Nevertheless different basic characteristics for the two base metals above need always be accounted for.

Coefficient of Thermal Expansion: if a metal with higher thermal expansion (like austenitic stainless) is the outer part of the joint where the inner part is a lower expansion metal (like carbon steel), clearances that are correct for allowing capillary flow at room temperature become excessive at brazing temperature.

Interchanging the materials in the same configuration (outer in place of inner material) risks to close the gap at all at brazing temperature: this should be avoided.

Thermal expansion differences should be known and used to obtain the correct gap at brazing temperature.

The brazing filler metal must be compatible with both base metals: this generally means that no brittle intermetallic compounds should be formed. If corrosion or oxidation resistance is needed, the properties of the filler metal in service conditions should be known.

In the proposed combination above, the stainless material (depending on the actual type) has some corrosion resistance to atmospheric exposure, while the carbon steel, lacking it, must be provided with a suitable protection (oil, paint or plating).

Galvanic couplers susceptible of promoting crevice corrosion, should be avoided. The ferritic, non hardenable stainless steel type 430 is known to be subject to interfacial corrosion when brazed with most silver based filler metals. A special silver base brazing filler metal containing nickel and tin, AWS BAg-21, was developed to avoid corrosion with this material.

Thorough cleaning of the elements is required as usual before brazing. Depending on the heat application method used, a suitable flux may need to be applied because heating in air develops surface oxide that interferes with brazing.

For austenitic stainless steel (300 series type) many fluxes are suggested as suitable, differing in the activity temperature range, typical ingredients and form (liquid, powder or paste). See AWS A5.31 - Specification for Fluxes for Brazing and Braze-Welding.

Fluxes are available as commercial brands. One should select and test a product compatible with the filler metal selected and, in the case above, suitable for all brazeable ferrous metals (except those with aluminum or magnesium).



Of the different brazing filler metals available, the ones based on silver have lower brazing temperature than those based on copper and should be preferred whenever possible.

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Stainless to Cast Iron Welding

Q: How can one weld austenitic stainless steel to gray cast iron?

A: Much depends on the configuration of the intended joint, on the thickness andconstraints and on the process being used. Assuming that the SMAW (ShieldedMetal Arc Welding) process is used, one should first clean and preheat the castiron. Then one should deposit on it a buffer layer either of stainless steel (type 309 or 312) orof nickel base alloy (ENi-CI). This procedure is called buttering. The main concern is avoiding cracks.

The technique should concentrate in melting the minimum of base metal, byintroducing the least amount of heat, with the smallest electrode and the leastcurrent, with thin weld beads. The weld is built up with additional beads (afterslag removal) until finished, without cooling down.

Finally the austenitic stainless steel is welded to the buffer layer. Slowcooling down to room temperature is obtained by providing insulation to the castiron or by cooling in a furnace.

An interesting supplement to the above presentation was published in a note by Damian J. Kotecki, Technical Director at the Lincoln Electric Co. and President of AWS, on page 14 of the March 2006 issue of the Welding Journal.

It is reported that, due to dilution with high carbon Cast Iron, weld metal from 309 or even 312 stainless steel electrode risks cracking because the composition of the deposited root pass layer results without any ferrite.

Even if cracking is avoided by suitable preheating, both the weld metal and the Cast Iron heat affected zone result rather brittle.The problem stems from the carbon in the Cast iron combining with the chromium in the stainless (309 or 312) to produce, in the resulting weld metal, networks of eutectic chromium carbides in austenite.

A better suggestion would be the use of electrode ENi-CI per AWS A5.15.Due to the complete absence of chromium from the composition of this last electrode, significant chromium carbides will not be produced.

Furthermore this electrode would promote spheroidal graphite formation in the nickel base alloy, and also lower hardness results in the weld metal. However, even if cracking during welding is avoided, there is still the danger of cracking being produced later by shock loading due to the intrinsic brittle nature of the boundary layer.

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Cast Iron to Mild Steel Welding [From PWL#025, Section 3]

Q: - How should one weld Cast Iron to Mild Steel?

A: - Cast Iron is an alloy of iron, carbon and silicon. Other elements may be added



for special purposes.

Gray Cast Iron, is probably the most common type. With slow cooling,its excess carbon solidifies as flakes of graphite. Its chief advantages are easy machinability, good damping capacity (to absorb vibrations) and relatively low cost. It is divided in further classes according to typical mechanical properties. Some types highly alloyed and with improved mechanical properties can be considered unweldable.

Ductile Iron, due to special additions to its chemical composition, presents graphite in spheroidal form and has the highest strength and ductility of unalloyed cast irons.

Malleable Iron is obtained with a long and specific annealing treatment that transforms iron carbides from white cast iron into irregularly shaped graphite nodules.

White iron, that is produced by rapid cooling from the solidification temperature, contains most of its iron carbides untransformed, is very hard and brittle and practically unweldable.

The mild steels to consider should have limited content of Sulfur and Phosphorus, which are known to contribute to hot shortness or the formation of cracks at the time of solidification.

Cleanliness and weld preparation is always most important.It is known that welding might produce brittle structures and in general reduce the mechanical properties of cast iron. However successful welds can be performed for useful purposes if one acknowledges the limitation introduced by the processes.

A successful welding process should not cause the formation of cracks during or after welding and should not introduce harmful or excessive residual stresses.

There is not a single welding process capable of welding successfully any conceivable combination of iron castings and steel. Furthermore one cannot point to a single filler metal rod or electrode to cover all possible cases. Therefore the problem is not simple.

Furthermore small iron castings behave differently than large and massive cast pieces. The mass has a great influence on the self quenching capacity of the parts and on the cooling rate after welding, directly affecting the obtained structures.

Any welding process produces two zones that undergo important structural transformations:

The weld metal is that portion of base and filler material that were melted by the welding heat, were thoroughly mixed and then solidified quite rapidly.The resulting structure is mainly a function of composition. As the dilution of cast iron into the melt contributes a large proportion of carbon that is responsible for the hard and brittle phases resulting during solidification, due attention should always be employed to melt the minimum amount of cast iron.

The heat affected zone although not melted, was heated to high temperature by the nearby weld heat. Most of its carbon, that was in form of graphite, went into solution in the phase called austenite. Upon rapid cooling this carbon enriched austenite transforms to the hard phase martensite, which is brittle and susceptible to cracking.

To control the properties of the heat affected zone, to reduce hardness and shrinkage stresses, one has to reduce the cooling rate. This is usually achieved by preheating the iron casting, either locally with a flame, if it is very large, or preferably in a furnace. And then, after welding, by letting it cool slowly, having wrapped or buried it into insulating material, or again in a furnace.



Preheat will also control the structure of the weld metal itself to the point that the formation of martensite is minimized or avoided at all.

However, small castings can be welded sometimes without preheat if the results are acceptable. Alternative techniques consist in welding thin and short beads. Subsequent beads temper the hard structures generated by previous ones.

To reduce and redistribute residual stresses, peening of the still hot bead with a rounded ballpeen hammer should be performed. Further weld passes contribute to interpass heating that helps in preventing too rapid cooling.

In general one should try to heat to the least possible peak temperature, to introduce the minimum heat, using small electrodes and low currents, to apply suitable preheat, to control interpass temperature and to study the performance of different types of filler material until the satisfactory selection is found.

The consumables available for welding cast iron are quite varied.Filler Metals of different types can be used for welding cast iron to mild steel. The selection should be based on ease of performance and on the acceptable results achieved. Once the main factors are understood and taken care of, practice and trials can tell which is the most economic and best solution for any particular case.

When using SMAW, the steel electrode (ESt) will give a very hard weld,non machinable, useful only for very small repairs.

Standard low hydrogen electrodes like E7018 have been used successfully, provided they were dried thoroughly to minimize moisture content.Even iron powder containing electrodes like E7024 were employed with good results.

Cast Iron electrodes (E-CI) with about 2.0%C, provide a structure similar tothat of gray cast iron: the weld metal is likely to harden unless proper provisions are put in place.

For difficult cases conducive to cracks, using Ni-Fe electrodes (ENiFe-CI or ENiFe-CIA) with about 50 %Ni- 50% Fe is probably the best selection for the dissimilar welding of cast iron to mild steel, although not the most economic.

If a more ductile or machinable weld must be obtained, high nickel electrodes (more expensive) can be tried, like ENi-CI or ENi-CIA, that will result in a soft, ductile and machinable deposit.

If a more strong weld is needed, for example for nodular irons of elevated mechanical properties, ENiFeMn-CI can be used, where the addition of manganese improves strength, ductility and resistance to cracks.

The electrodes included in the AWS Specification A5.15 are not the only onesavailable. Proprietary electrodes, not classified with AWS, are available with improved properties for special applications. In difficult cases it may be worth to seek advice from electrode manufacturers, to experiment and to check results.

For certain production lines, higher deposition rates than those available by SMAW (with covered electrodes) may be preferable. In these cases GMAW (Mig) has been applied successfully, especially for ductile or malleable iron.

The wire composition is similar to that used with covered electrodes. Steel wires of types ER70S-3 and ER70S-6 have been used and also ERNiFe-CI.Also nickel containing wires (high nickel, nickel-iron, nickel-iron-manganese) are being used. All other precautions should be in place as necessary.



This presentation would not be complete without including also the solutions that employ the oxyacetylene flame. The slower heating rate of this process causes a larger heat affected zone to form but effectively avoids the development of brittle martensitic structure. Consumables are cast rods with higher levels of carbon and silicon than the castings.

RCI, RCI-A and RCI-B are used respectively for gray cast iron, higher strength alloyed iron, and for malleable and ductile iron. Suitable fluxes must be used to protect the molten metal from oxidation. Preheating must be provided. Slow cooling must be ensured.

Besides welding, in certain cases it would be useful to consider also braze-welding as a possible solution. See Braze Welding. Here the filler metal is copper base and the cast iron is not melted. Less heat, less distortion, less cracking, machinable filler metal and generally adequate strength is provided. The most serious difficulty, that may sometime prevent its adoption, is the color mismatch of the braze-welded joint.

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Repairing a Crack in Cast Iron

Q: How is a Crack repaired in a gray Cast Iron?

A: A special section addressing this question has been included in the WeldingAdvisers Site. Click on Welding Cast Iron.

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Welding of AISI 1141

Q: Can an AISI 1141 cold drawn rod be welded to an ASTM A572 Gr.50 plate?

A: Fusion welding should not be attempted. AISI 1141 is resulfurized forincreased machinability (free machining). Sulfur causes hot shortness producingcracks. In certain cases it could however be friction welded, if strengthrequirements are limited.

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Welding of 1018 to 4140 [From PWL#061]

Q: - How is 1018 welded to 4140?

A: - Welding 1018 to 4140 is possible although one should know more about the application, because the differences between the two steels may cause consequences one may not want to get.

1018 is a mild steel weldable without problems and not hardenable except by diffusion surface treatments like carbonitriding which need not concern us here.

4140 is a chromium molybdenum low alloy steel with medium carbon content (about 0.40%) that can be hardened by direct quenching and tempering. It can be welded but with special precautions like preheating, to slow down the cooling rate.

Without preheating, fast cooling after welding generates martensite, a hard



structure that risks to develop cracks near the weld.

Welding a soft steel to a hard steel can be useful in certain cases, for example if a handle needs to be joined to a hard implement. One should understand that the handle will not become stronger, and that the implement, if it was heat treated to a high strength and hardness before welding, will become weaker near the weld, because of the heat.

Two contrasting things will happen because of the localized heating of welding. On one hand all the volume heated, next to the weld, to a certain temperature up to the so called transformation temperature (say up to about 750 0C or 1400 0F) will become weaker due to annealing, effectively eliminating the higher properties due to heat treatment.

But very near to the weld itself, the temperature will exceed the transformation temperature. The material structure will change into "austenite", hardenable upon cooling once the welding process is stopped. Not only will the material become very hard in a thin strip near the weld, it might also crack.

Suppose we can preheat with an oxyacetylene flame and that we want to weld by SMAW (or stick) with an electrode of almost any usual type.

If we know what to expect, that our mild steel handle at the weld will be weaker than the hardened implement, and if this is OK for the application, we should heat with a flame, before welding, the 4140 implement where we want to place the weld.

By so doing we avoid cracking. The full hardness of our implement will still be present in the part at some distance from the weld (say at 50 cm or 2", depending on thickness, on the size of the weld and on the amount of heat input).

We should again heat the weld with the flame, to temper or soften any martensite that could have formed in the process (Local Stress Relief). If that is what we need, that is what we get.

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Welding a splined End onto a hardened AISI 4140 Shaft

Q: How do I weld a splined end to a 4140 shaft hardened to 28-32 HRC?

A: The best process would be Friction Welding.

It is rapid and economic, its preparation is simple, it interests the whole section, it probably would not need reheat treatment.

But some of the length is consumed, and flash has to be removed. Concentricity may be a concern. For details on the Process and on the Equipment of Friction Welding click on Friction Welding Process and on Friction Welding Equipment.

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Welding of AISI 440C

Q: How can an appendage be welded to an implement made of stainless steel 440C?



A: It cannot, because 440C is not weldable. One can select a different solution:

Mechanical fastening, Adhesive bonding if the usage temperature is compatible with the adhesive, High temperature brazing integrated with heat treatment, or Redesigning the implement with integral appendage.

See Welding Stainless Steels in the Welding Advisers Site. Click on Welding Stainless Steel.

Again on Welding AISI 440C

Q: We need to attach a .080" thick 1045 sheet stock part to a hardened part (RHC 58-62) that has a bearing race on it. The preferred material for this part is 440C. A corrosion resistant material is needed. The weld joint is a slip fit at this time with fillet welds on one side and seam welds on the other. Can Hardened 440C be welded successfully to a dissimilar material?

A: No. Unfortunately 440C is unweldable. We already treated this matter.

As the material 440C, a very hard stainless steel, cannot easily be replaced, one has to look for an alternative joining method. Given the slip fit of the assembly, it seems that the best solution would be adhesive joining. The adhesive and the clearance have to be selected with care, following adhesive manufacturers' recommendations.

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Weld repair of nitrided tools

Q: How can tools made of nitrided tool steel be repair welded?

A: Nitrided layers should first be mechanically removed, for a depth at leastthe double of their original nominal thickness.

Then welding can be attemptedbut its quality may be questionable because of diffused nitrogen even deep inthe tools.

For information on Welding of Tool Steels click on Welding Tool Steel.

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Process Comparison

Q: A butt weld has to be performed on short lengths of sheet metal. It could be done by Plasma Arc Welding, by Electron Beam or by Laser Beam Welding: which process should be preferred?

A: Given the availability of different processes, once the quality requirements are satisfied, the most economic one should be selected. The economy of performance, expressed as cost per weld, has to be calculated by taking into account all the expenses for equipment, consumables, workforce, handling etc.

A first evaluation can be done by comparing advantages and disadvantages of each process in turn. If manual and automatic operation can be performed, the cost of both should be estimated.

(Note: See as a Guide our page on Welding Cost Estimate).



Plasma Arc Welding (PAW):

Advantages of PAW as compared to GTAW:

Higher energy concentration, higher heat Improved arc stability, especially at low current Greater arc length tolerance Greater plasma and welding speed, shorter weld time Tungsten contamination eliminated Less skill required for manual welding For larger thicknesses welding in one pass with Keyhole technique Smaller weld volume, less filler metal than with GTAW. Reduced rework and rejections.

Disadvantages:

Equipment more expensive than Gas Tungsten Arc welding but much less than EBW.

Short life of orifice body, requires replacement. More welder's knowledge required Higher rate of consumption of inert gas.

Electron Beam Welding (EBW)

Advantages:

High energy heat source, for deep penetration in thick narrow joints Filler metal usually not required Total heat input lower that for arc welding, limited deformation Welding in vacuum, ideal for reactive metals Difficult-to-weld materials can be joined. Elevated welding speed Beam shape, focus and path controllable by electric and magnetic lenses Automatic beam tracker available Permits solution to otherwise impossible procedures

Disadvantages:

Expensive equipment including vacuum chamber and pumping system Beam sensitive to occasional magnetic fields Unproductive pump down time required Shielding against harmful by-product x-rays required Precision set up required with special fixtures

Laser Beam Welding (LBW)

Advantages:

High power density heat source, for deep penetration in thick narrow joints Welding performable in air (depending on materials) Total heat input lower that for arc welding, limited deformation Easily mechanized high processing speeds with very rapid stopping and

starting Micro welding possible, precise welds can be obtained. Difficult-to-weld materials can be joined. No electrode or filler materials are required. Welds with little or no contamination can be produced. The laser beam can also be time shared.



If a weld can be done by both EBW and LBW, (with limited power) the last one is more economic as vacuum system is not required

Hybrid systems available combining LBW and GMAW

Disadvantages:

Limitation on power available (affecting thickness) for solid state systems Capital cost more expensive than power arc welding systems. Even more expensive high power sources for welding thicker materials Additional shielding provisions required for reactive metals Safety concerns for operators' vision protection Precise fit up critical Low electrical conversion efficiency The penetration is less than for EBW The power at the workpiece will be significantly reduced due to reflection

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Carburize with Oxyacetylene Flame?

Q: Is it practical to use an oxyacetylene torch to raise the carbon content of mild steel in an attempt to carburize the mild steel for case hardening by heating and water quenching?

A: Unfortunately no. What can be done instead is "pack carburizing" in a stainless steel box. Proprietary products made for this purpose, contain besides carbon (in the form of charcoal and coke) also other important ingredients (carbonates of barium, calcium, sodium) called energizers.

Parts are buried in the granular carburizing product, the box is closed with a cover and loaded in a furnace at about 850-900 0C (1560-1650 0F) for 4 hours or more, depending on the depth of case required. If parts can be removed quickly from the granules they may be then quenched immediately in water. Otherwise the box is slowly cooled in the furnace and then the parts are reheated for quenching.

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Fillet welding of Rimmed Steels

Q: Why is Fillet welding preferred for Rimmed Steel?

A: Rimmed Steel manufacturing processes provide a case or rim of very cleanmaterial free of defects. Conversely impurities tend to concentrate in themiddle section of ingot or billet.

This feature persists through the rollingprocess, so that plates of this kind tend to have their central core less cleanthan the superficial layers. This property provides and advantage when designcalls for fillet welding, which does not penetrate to the center of the plate.

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Manufacturing a Spherical Vessel

Q: What is the normal method of manufacturing a welded spherical pressure vessel?



A: Assuming quite a heavy wall spherical pressure vessel of large dimensions, the material and the thickness of the plates are to be selected depending upon service pressure and conditions.

The vessel will be manufactured by welding together prepared sectors.The dimensions of the sectors will depend upon the size of the press available in the workshop for hot forming the plates in special dies.

On the drawing table, (or on the computer screen) the sphere is divided into two hemispheres. Each of them is again divided in four, six or more sectors depending on their dimensions. Two caps shall be located at the poles.

One single sector has to be designed in detail: they will all be equal. Some material has to be added at the margins for precision cutting and chamfering after forming and stress relieving.

Depending on material, dimensions, process etc., the sectors have to be prepared for welding together once the joint details have been established. If clad material is used (i.e. a carbon steel with a thin layer of stainless steel) special welding procedures must be developed and tested.

Inlets, outlets, manholes and whatever passages are needed, are designed to be performed at the proper stage in the process.

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Use of Low Hydrogen Electrodes

Q: We are requested to weld with Low Hydrogen Electrodes. Why?

A: Hydrogen gas is readily absorbed because of its high solubility in molten andhot steel, but it is rejected at lower temperatures as solubility decreases.Furthermore when dissociated in atomic form, hydrogen can diffuse in the HeatAffected Zone.

A detailed discussion is included in the page on Weld Cracking: click on it.

Two kinds of defects can be generated by hydrogen in welds. Porosity is thepresence of gas bubbles that weaken the structure, trapped in the solidifyingmolten metal. Cracks, even delayed long after the end of welding, are generatedin weld or heat affected zone as a consequence of recombination of atoms tomolecules and pressure raise.

Hydrogen is particularly harmful in strong, hard, crack sensitive hardenable orstructural steels, especially when high residual stresses are present or whendesign is rigid and most constrained.

The use of low hydrogen electrodes, kept dry before use, with proper proceduresincluding pre- and postheating, is mandated by the need to provide measures aptto prevent the dangers outlined above.

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Strength of Stainless Steel Spot Welds

Q: How to judge of the adequacy of Spot Welds in Stainless Steel Sheets?

A: Austenitic Stainless Steel sheets are easily spot welded. However, just



byobserving how many common household implements made of stainless steel failsometimes in spot welds, one would think that it may be difficult to obtainadequate strength and to evaluate it.

Given standard single lap spot weldcoupons, it appears that the minimum strength reported for each spot weld inaccepted Specifications has no real interest, because good spot welds will notbreak in the weld. When tested in tension they will rather fail in the materialaround the weld, by tearing a button in one half of the specimen and leaving ahole in the other half.

This is a good result even if the tensile test value atrupture is not known exactly.

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Sorting unweldable Stainless Steel

Q: A batch of regular stainless steel fasteners to be welded on a sheet, wasinadvertently mixed up with free-cutting stainless ones. As we are told thatfree-cutting stainless is not weldable, how can we sort out the weldable items?

A: Hopefully the batches, although unknown, are still separated: if this is thecase you need only to examine representative specimens of batch A vs. batch B.It is quite straightforward to sort the types by microscopic examination, aftergrinding and polishing one surface of each one (a nondestructive process): thefree-cutting material is peppered by sulfur particles readily standing out ofthe background. Alternatively you may try to weld: the non weldable will crackright away...

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Welding Thin Stainless Steel Sheets [From PWL #32]

Q: Gas Tungsten Arc Welding thin sheets of austenitic stainless steel type 304L results in unacceptable distortion. What can be done to improve results?

A: Compared to carbon steels, austenitic stainless steels have higher thermal expansion and lower thermal conductivity: these are the main reasons contributing to unacceptable distortion.

GTAW is a proper process to weld such jobs but, due to the low current employed, manual operation may be difficult to control. Better results could be obtained by mechanized welding.

Other precautions include proper fixturing, pulsed current if possible and step welding. Good cleaning and preparation are always important.

Constant current, non pulsed power supplies of drooping-voltage characteristic are used with direct current straight polarity, electrode negative. Pulsed current may provide better weld control to avoid burn through.

Most widely used tungsten type is that with 2% Thoria (EWTh-2). High frequency should be used to start welding and to avoid contamination due to electrode contact with the weld pool. Argon is used as the shielding gas.

The conical electrode tip can be ground with different apex angles. A narrow angle of about 15 to 30 degrees tends to produce a relatively wide bead with shallow penetration. A larger angle of 60 to 75 degrees would give a narrow bead with



increased penetration.

Thin gage stainless steel sheet should be properly clamped and aligned to avoid buckling. Fixturing of the abutting edges, with no gap for thickness up to about 1 mm (0.040"), is done with copper chill bars, usually nickel plated.

The backside chill bar includes a groove, placed under the joint, where argon can be provided to prevent backside oxidation. The two front side chill bars should be beveled to make room for the torch.

Good contact between stainless and copper bars helps in removing excessive heat.If the clamp down bars are very close to the line of welding and held with considerable pressure, a compressive force will act on the seam while welding, as lateral expansion is prevented. The upsetting force will reduce shrinkage stresses and distortion.

Tack welding should be provided at close intervals but with a proper sequence that will maintain alignment.

Pulsed current if available may be advantageous in reducing heat input. Current is pulsed at regular intervals between a background level and a peak level. A stable arc is more easily maintained.

In case of long seams, short welding stretches should be performed, at relatively far locations, taking care to let the joint cool down between welds.The start and stop of each weld and the tack welds should be ground to eliminate possible flaws in those places.

Implementing most of the above precautions should result in weldments of reduced and acceptable deformation.

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Stainless Steel Tanks for Water[From PWL #79]

Q: After 7/8 years of service, some of my SS 304 tanks are corroded at HAZs & pinholes are observed in hydrotesting. I want to weld repair it. Please help.

A: Thank you for your question. Note that the letter does not mention if the tanks keep water or any other more corrosive liquid.

If the material is indeed SS 304, one should have known from the time of manufacturing that the failure is only a question of time. The problem is "sensitization" of 304 as explained in my page http://www.welding-advisers.com/Welding-stainless.html

A more suitable selection would have been 304L or 321, if indeed the tanks are for water. Now whatever repair you may do, it will last only so much time, because heating 304 in the interval between 600 and 900 0C (on both sides of the weld) will cause the basemetal to become prone to corrosion. Sorry, there is not much to do by welding. Patching up using metal strips adhesive bonded on the leaks or other caulking solutions may be possible. Next time ask before manufacturing.

Note: - The preferred filler metal for welding 304L is 308L. For welding 321 (which is "titanium stabilized"), the filler metal is 347 ("Niobium stabilized")



While not practical for welded tanks or sheet metal constructions, there is a way to eliminate the chromium carbide precipitation ("sensitization") by performing full solution treatment of 304 small implements (bars or tubes), at 900-1100 0C (1650-2010 0F) followed by rapid quenching in water. This process however must contend with problems of heavy oxide formation if not done in vacuum or protective atmosphere, and of distortions. Therefore it is not practical for large structures.

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Repairing Holes in Aluminum Panels

Q: How can we conduct annealing of 7075-T73 and 2024-T62, wrought and formed sheet respectively, welding some holes up and reheat treating?

A: Forget it. The materials indicated are not weldable by fusion welding.Also heat treatment cannot be performed easily: even with most apt facilities, the deformations following re-solution heat treatment, quenching and aging would most probably cause scrapping of the parts.

The holes should be enlarged and carefully machined to some simple geometric shape (circle, square with rounded corners, etc.). If both sheet sides are reachable one can prepare machined patches. The patches, of the same materials and condition, could be of double the sheet thickness. In the center the selected shape should be machined to stand out in relief, to fill the hole. This shape should be emerging from the rest of the patch, machined to present wide margins of the same thickness as that of the sheets.

The patch so prepared and thoroughly cleaned has to be put in place from the back side, so that the hole is filled flush by the relief shape machined in the patch. The patch can be then resistance welded in place along the line running in the margins at mid distance between the raised shape and the patch border. If the patch has to be leak proof then seam or overlapping spot welding has to be performed, otherwise separate spot welds may be sufficient.

If only the outer side is reachable then a simple sheet patch can cover up the hole and be adhesive joined in place.

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Welding of Brass Sheets

Q: How should brass sheets be welded together?

A: Although welding of brass sheets is feasible, one should explore theadvantages of brazing instead. Brazing is performed at lower temperature withless deformation and, with adequate joint design, can develop considerable loadcarrying capacity.

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Brazing Fittings

Q: During torch brazing of a fitting onto a steel tube, it was found that thesilver alloy filler covered the surface only in part, making the jointunacceptable. How can we improve?

A: First, the clearance between the elements should be correct,between 0.05 and 0.10 mm (0.002" and 0.004") on the side.



Second, both surfaces must be absolutely clean from dirt, paint,rust and oil or grease even when a flux is used.

Third, rotating gently one element relative to the other fora quarter of a turn to the right (or to the left) and back while the braze isstill liquid will most probably improve the results.

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Furnace Brazing of Tubular Joints

Q: What are recommended practices for furnace brazing of tubular joints?

A: Cleanliness is the single most important prerequisite for successful brazing. The use of suitable preforms, that is of prepared units of formed brazing alloy of definite shape and weight for a specific application, may contribute to improve quality and reduce costs.

The selection of the suitable filler metal should be adequate for joint and process requirements. An indication on usability of different silver brazing alloys was given in a note published in section 4 of Issue 003 of Practical Welding Letter for November 2003. Click on PWL#003.

Radial clearance of the capillary space should be calculated to be between 0.050 to 0.125 mm (0.002 to 0.005") at brazing temperature.

The brazing filler metal preform should be possibly located at the recessed side of the joint, so that the free side of it can be visually inspected for uninterrupted presence of the flown brazing alloy, indicative of an adequate brazed joint.

For designing Brazed joints with confidence one should learn the lessons of the following publication.

ANSI/AWS C3.3:2002 Recommended Practices for Design, Manufacture, and Inspection of Critical Brazed Components American Welding Society, 01-Jan-2002 32 pages Click to Order.

For an informative list of useful Brazing Resources available online, interested readers are reminded to consult again the Mid July Bulletin of the Practical Welding Letter at PWL#035B.

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Brazing in Steps

Q: A complex assembly to be furnace brazed requires complicated fixturing. How could the preparation be simplified?

A: By breaking down the assembly in a logical sequence one can divide the brazing operation in two or more simpler stages. One has to select appropriate filler metals in progressively descending order of brazing temperature.

In this way the subsequent furnace brazing temperatures do not impair previous brazements. A secondary gain to be considered is the longer time available for



assembling after cleaning operations. This time is limited because harmful oxides form on metals even at room temperature, disturbing wetting and brazing.

Performing the brazement in steps allows preparation in shorter times, contributing to the brazing success. Even brazing repair, should it be necessary, is easier in partial assemblies.

Another way of simplifying fixtures consists in designing self fixturing (or self-jigging) provisions, that is built in temporary means (clamping, crimping, expanding, press fitting etc.) of keeping parts in place until brazing is completed. Brazing filler metal is usually preplaced in the joint or near to it. A capillary clearance is always required.

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Leak Test

Q: X-Ray inspection of a repair weld on a pipe seems to indicate that porosityis OK, but pressurizing shows moisture around the weld edge. Where does it comefrom?

A: A suitable form of Leak Testing is recommended, depending on the application.It could be a simple bubble testing, with air or other gas pressurized inside,while the container is submerged under a liquid.

Or using Liquid Penetrant, either before or during hydrostatic tests, as amarker for detecting leaks.

More sensitive specific gas detectors could be applied in exceptional cases.

See Metals Handbook - ASM InternationalVol. 11 - 8th edition - Nondestructive Inspection and Quality Control or Vol. 17 - 9th edition - Nondestructive Evaluation and Quality Control

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Class A Welding

Q: Which welding does Class A refer to?

A: AWS D3.6M-99 Specification for Underwater Welding American Welding Society, 01-Apr-1999, 129 pages Click to Order, presents four different Types or Classes:

Type A welds are characterized by requirements ensuring an underwater weldcomparable to a surface weld. Usually dry (hyperbaric) underwater welds meetthese requirements.

Type B welds refer to wet underwater welds. They define less criticalapplications with reduced ductility and increased porosity.

Type C welds have even less requirements than type B welds for applicationswithout load bearing functions.

Type O welds present requirements of surface dry welds, as well as those ofother Codes and Specifications.



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Hardening Heavy Sections

Q: A bar of high carbon steel (0.70-0.90 %C), of 100 mm dia. (~4"), quenched inoil from elevated temperature, failed to harden. Heated again and quenched inwater, its hardness did not improve. Why?

A: A heavy bar of plain high carbon steel cannot develop substantial hardnessupon quenching because heat removal is too slow due to its substantial mass.

Sluggish heat removal prevents martensite (the hard constituent) to form andpermits less hard structures to appear, during the transformation fromaustenite. If ~60 HRC hardness is needed, one must switch to air hardening toolsteel like SAE A1, where the composition allows slow cooling to produce fullhardness. Do not forget tempering.

However, if only surface hardness is required (and the core may remain softer),one can still use plain high carbon steel, by localized intense heating throughinduction hardening (or possibly laser or flame hardening) and rapid quench. Tempering is always required.

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Furnace Hardening of Steels

Q: A medium carbon (0.35 %C) steel bar 1" dia. (25 mm), did not give substantialhardness when quenched in water from an air furnace at 820 oC (1500oF). Why not?

A: The problem is probably a consequence of carbon loss (decarburization) due tothe reaction of air in the furnace with the surface carbon of the bar; ineffect, locally, one gets lower carbon steel, less capable of hardening whenquenched.

A protective atmosphere in a furnace of different type would probablyovercome the problem. Alternatively one could adopt an old trick, by putting thebar in an air furnace but in a stainless steel box full of charcoal orproprietary products, to counter the harmful influence of oxygen in air.

The barmust then be withdrawn quickly for quenching as needed.

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Heat Treating Tool Steel in a Bag

Q: Can occasional Tool Steel Heat Treatment be performed in Air Furnace?

A: No. Heating High Carbon Tool Steel in Air Furnace will cause decarburization (loss of surface carbon) that will substantially reduce thesurface hardness obtained upon quenching. Oxidation too is generallyobjectionable. In fact the higher the carbon content, the most significant thedecarburization process will be, and tool steels generally contain high carbon.

For occasional heat treatment of tool steels in an air furnace one can use air tight bags manufactured of stainless steel foil. These are made bymultiple folds at the overlapping edges or by seam welding. The tool isintroduced in the bag, most of the air is then removed by enveloping the tool astightly as possible in the bag. A tiny



hole must be left in the closed bag,usually by putting in the last fold a fine nail that is later withdrawn, for theresidual hot air to find a way out.

The bag will then protect the tool from oxidation and decarburization duringheat treatment in the air furnace.

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Normalizing welded Mild Steel [From PWL#057, Section 3]

Q: - We have been asked to normalize the welding on a unit that is made up of 4 types of mild steel. It is our understanding that normalizing is normal with 4130/4140 material for stress relieve and strength, but that it does nothing for mild steel. Can you verify this? Or do you have any documentation to verify it one way or the other? Thank you.

A: - Normalizing is a concept used sometimes quite loosely.The official ASM description of the term Normalizing is:"Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range."

If you mean heating mild steel above transformation point to austenite and cool in air, you only get stress relieving. The same result can be obtained at 650 deg C (1200 F) which is below transformation.

Nothing will be gained at a higher temperature, only more scale to remove. If in the assembly also 4130/4140 are present, depending on their thickness (which reflects the rate of cooling in air) some strength will be gained.

In order to avoid misunderstandings it is recommended to ask the customer for written instructions concerning heating temperature and time, and have him/her pay for the process performed.

To learn more on Normalizing see the following article: The Importance of Normalizing fromIndustrial Heating.

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Grinding a Plate and its Distortion

Q: A hardened steel plate was reasonably flat after heat treatment.However, after grinding from one side as needed, it distortedbadly. What should be done to prevent deformation?

A: The hardened plate is subjected to internal stressesin equilibrium, (tension and compression) symmetricallydistributed from both sides of the mid plane. By grinding from one side only, equilibrium is disrupted.

The remaining stresses rearrange in such a way that producesdistortion. The remedy would be, if possible, to grindsymmetrically from both sides.

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Preventing Distortion[from PWL #66]



Q: I have a question regarding welding angular distortions in butt-welded stainless steel plates. I have done some experiments for plates with dimensions 150*200*2 mm, but something strange has happened. Some of my plates have distorted upward but the others have distorted downward. The welding conditions have been the same for all of them.

A: Distortion is the consequence of residual stresses set in by welding. Especially for manual welding, it is almost impossible to determine if welding conditions were or not exactly the same.

Taking into account that distortion will be always greater in stainless steel than in regular carbon steel, to reduce or prevent distortion in the simple setup described in the question above one should consider the following recommendations.

Use a joint configuration based on welding from both sides (X-joint), requiring less filler material and less heat input, instead of a simpler design welded from one side only (V-joint).

The recommended configuration above is also more symmetrical than the discarded one, and therefore it is likely to introduce more balanced residual tensile stresses.

Reduce as much as possible the root opening and, if applicable, the bevel angle, again to reduce filler material and heat input.

Restrain the plates in a heavy fixture and introduce compressive stresses by peening the joint with a hammer while the weld bead is still hot.

Preset the plates at an angle before welding (open like a book downward, more than needed to have the pages flat in the same plane). Residual stresses will pull the plates back in the same plane after cooling down.

Try to use block and back-step progressions to balance and reduce residual stresses and resulting distortions.

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Straightening a Warped Beam

Q: How can we straighten a warped beam?

A: You can use an oxyacetylene flame. The purpose is to introduce in the beam carefully planned tensile stresses to pull the beam straight. You know from our page on Welding Distortion that residual tensile stresses form because of local thermal expansion. The explanation is as follows.

Stresses are due to volume changes with heating and to decreasing yield strength at elevated temperature. Metal subject to thermal expansion while heated tends to be compressed by the surrounding cool structure. The heated volume has lower yield strength at high temperature, and then it is easily upset to shorter dimensions.

Upon cooling the same material tends to contract in all directions and is now stressed in tension by the attached cool structure which did not move appreciably in the process.

By now the yield strength is again higher, at lower temperature, so that the upset material cannot regain its original dimensions.The result is the development of residual internal tension stresses in the weld.



By selecting the convex portion of each bend and applying sufficient heat (in steel: to bright red) to a suitable amount of material, one can cause sufficient tensile stress to redress the beam. The careful selection of the location of heating is critical, and the amount of applied heat is what determines the success of the operation.

The practice can be repeated for other areas nearby until the result is acceptable. One should take care not to heat the whole beam too much because that interferes with the purpose of straightening.

What works for a beam works also for a surface presenting unwanted bulges. The principle is the same, to introduce two dimensional residual tensile stresses by heating up the convex portion of the deformed plate. A word of caution is necessary when dealing with stainless steel. One should beware of heating in the sensitization temperature interval. (See on this subject Stainless Steel Welding)

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Spot Welding Dissimilar Materials

Q: Can dissimilar materials be spot welded together?

A: The short answer is yes, but it may be neither simple nor advisable in certain cases if brittle structures are produced by the dissimilar metals mixing in the molten nugget.

In particular austenitic stainless steel and carbon steel are not usually spot welded together because the resulting nugget structure risks to be hard and brittle, although it could be studied and modified using the Schaeffler diagram and specially conceived heat treating cycles.

Materials having widely different properties require that a heat balance be achieved by compensation. The more conductive material, electrically and thermally, must be heated more as it provides less resistive heat, and the heat is lost more easily by conduction.

A common technique uses an electrode of smaller face diameter and higher resistivity facing the more conductive material, or by inserting a foil of poorly conductive material between them.

Concerning the number of sheets weldable with a single nugget, normal practice suggests not to exceed three layers, although four sheets are occasionally spot welded together. In any case the ratio of the thickest to the thinnest sheet should not exceed three.

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Projection Welding of Steel Nuts [From PWL#086, Sect. 3]

Some of the most interesting articles explaining basic welding issues are found quite often in short notes intended to provide answers to practical questions proposed by readers. I would like to give here the summary of such a note full of significant details, published at page 16 of the September 2010 issue of the Welding Journal.

In his note Donald F. Maatz Jr., member of the AWS Detroit Section Executive Committee and, among others, also of the D8 and D8D Automotive Welding Committees, states that, for many different audiences, when it comes to problems



regarding Resistance Welding, "projection welding always tops attendee's list of concerns".

The question in cause referred to the lack of published schedules establishing suggested parameters for the projection welding of steel nuts, to be used as a starting specification for the procurement of suitable equipment.

Having discussed the need of a suitable schedule for providing the necessary elements for the correct design of adequate equipment and tooling, the author acknowledges the current lack of a "robust set of welding schedule guidelines for the resistance welding of forged or coined projection weld fasteners".

It appears that the lacking data are part-specific and as such "not readily available to the welding community". The reason is that too many factors must be accounted for. Among them the materials of fastener and base metal, projection geometry, volume and number, substrate thickness, strength and coating.

The author then attempts to provide useful guidelines with the purpose to achieve tentative starting weld schedules to be refined with actual application trials. He suggests that the welding time should be less than what assumed from previous experience with sheet metal projection welding.

Then he remarks that the force required should be higher than what one may think, to assure proper contact and adequate forging pressure once the welding current has stopped.

He further notes that the welding current may need to be much higher than what presumed to be enough, and then the tooling must be able to carry that higher current and its controls must be suitable for fine tuning.

Finally he admonishes that the correct design of the fasteners projection plays an equally important role as the schedule for obtaining quality welds, and he plans to write a future article on this subject.

Interested readers are urged to seek the original article given above, where they can find also how to contact this instructive expert author.

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Welding together Different Carbon Steels [From PWL #45]

Q: I wish to weld different materials, ASTM A-36 and AISI 1045. The tensile strength is different, AISI A-36 Ts= 40-55 kg/sq.mm and AISI 1045 Ts= min 58 kg/sq.mm. What kind of filler metal will match both materials? Do we need preheating?

A: It is not the strength level but the carbon content of AISI 1045 that may make problems. Obviously the heat of welding will reduce the strength locally, but if the cooling conditions are such that martensitic structure develops in the heat affected zone then there is risk of cracking. Therefore you should use low carbon filler metal to dilute the carbon content of the weld and, depending on the mass involved and the process selected, you may need preheating, at least locally, to reduce the cooling rate (to avoid hard and brittle martensite) and stress relieving after welding (to temper hard microstructures and to reduce residual stresses).

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Welding Aluminum to Stainless



[From PWL #26]

Q: How is Aluminum welded to Stainless Steel?

A: It must be realized that fusion welding is generally not suitable for welding together dissimilar materials like aluminum and stainless steels. That is because of widely different melting temperatures, no mutual solubility in molten state, and because of differences in thermal conductivity and in thermal expansion that cause stresses and cracks.

During welding, low temperature melting phases and several brittle intermetallic phases are generated that compromise the integrity of the weld. Also not every aluminum type and not every stainless steel type can be considered for being joined together.

However a highly localized fusion welding process of elevated power density like Electron Beam Welding in vacuum may be sometimes used, provided that a third transition metal, compatible with both base metals, is used in between. In the specific case Silver might be used as a transition element, or to bridge the gap.

Solid state welding is applicable in certain combinations, providing acceptable joints can be realized that meet requirements. One of the most used of these processes is friction welding. Cleaning of the surfaces is of the utmost importance because contaminants entrapped in the joint risk to undermine its properties.

For joining large parts a suitable transition hybrid element (part of which is aluminum, the other part being stainless) can be prepared, welded by friction. The ends of the transition element can then be welded to the main structure parts by more conventional procedures between similar base metals.

Besides that, if alternative solution can be considered, brazing or adhesive bonding, if appropriate, are applicable.

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Welding Steel to Aluminum [From PWL #40]

Q: How is Steel welded to Aluminum?

A: A similar question was formulated involving Stainless Steel.

One should remember that the same obstacles already mentioned there hinder the proper formation of successful fusion welding of such dissimilar metals. These are: widely different melting temperatures, no mutual solubility in molten state, discrepancy in thermal conductivity and in thermal expansion that cause stresses and cracks.

Furthermore during fusion welding, but also during heating to some low temperature like 200 0C (400 0F) melting phases and several brittle intermetallic phases are generated that compromise the integrity of the weld.

If confronted with a similar problem, short of selecting a different material for one of the components, so that the combination be more favorable, one should explore which alternative process is suitable for the application.

Solid state processes like Explosion-, Friction-, Magnetic Pulse-, Ultrasonic-welding,



Roll bonding and High Temperature Diffusion joining avoid fusion by definition. Obviously not all of them can be suitable for a given application, because of the specific limitations of each one of them.

Other than those, High Energy like Electron- and Laser-beam welding could sometimes be applied as they are able to concentrate their energy in a very tiny spot limiting their influence in heat, location and time duration.

Finally, if the joint configuration can be adapted to process requirements, brazing, soldering or adhesive bonding might provide a suitable solution.

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Welding Copper to Stainless [From PWL #27]

Q: Can Copper be welded to Austenitic Stainless Steel?

A: Copper is readily welded to austenitic stainless steels with the Gas Tungsten Arc Welding (GTAW) by using suitable filler metals like ERCuAl-A2 or ERCu-Ni3. Welding is usually limited to thin sections, less than 3mm (0.13 in).

Buttering is not needed, especially for thin sections. The heat has to be addressed to the higher conductivity metal (Copper). Preheating at 540 0C (1000 0F) may be used to reduce thermal stresses on the finished weldment.

For Gas Metal Arc Welding, preferred for heavier thicknesses, the filler metals are the same as above, but one may wish to perform buttering by braze welding the stainless side to reduce dilution.

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Welding Copper to Stainless (B) [From PWL #56]

Q: I would like to have information on how to effectively weld stainless to copper. In particular the pieces have cylindrical shapes. The 2 parts to be joined are cylindrical (equal dimensions) ranging from 1 to 10 mm. Materials are copper and stainless (different grades).

A: It would be inappropriate to give a general answer. Depending on the actual shape of the joints, on the exact materials and on the application there are possibly a few techniques suitable to do the job. If you mean end to end joining I would start by trying friction welding: except for the smallest sizes where there might be some difficulty, for the others it should be OK.

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Welding Copper to Stainless (C) [From PWL #79 (4)]

In certain cases, see the report in PWL#079, cracks can be formed by Copper Contamination Cracking, a known cause of failure due to penetration of molten copper into the grain boundaries. Therefore it is suggested to perform preliminary trials to avoid the conditions leading to CCC.



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Welding Copper to Aluminum [From PWL #64]

Q: How can one weld Copper to Aluminum?

A: Copper and Aluminum are incompatible materials that cannot be fusion welded together. They can however be welded by solid state processes that do not heat the materials to melting temperatures.

Among these processes are friction welding, friction stir welding, magnetic pulse welding, ultrasonic welding, cold welding, explosion welding.

After having prepared bimetal transition parts, welded by a suitable solid state process, one can proceed with regular welding or brazing of additional components by matching the materials by type (copper to the copper side of the transition element, aluminum to the aluminum side).

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GMAW with straight CO2 gas

[From PWL #76]

Q: - I see a lot of GMAW being used around the place but they are using a straight CO2 gas. In my experience, we always used a CO2/argon mix gas which not only

produced a better weld, had less spatter also.

There also was some discussions with my American colleague who mentioned in the States they will not allow the use of GMAW with only CO2 (carbon dioxide) Gas.

Apparently there were some failures resulting from this process.

Is there anything to back this theory up and have you heard anything similar?

A: - The use of CO2 is not forbidden as far as I know, so that failures, if there were

any, may be due to other causes too. Gas selection is probably also a question of cost and of ease of supply, especially in developing countries.

You are right about spatter and quality, but if Welding Procedure Specifications (WPS) were approved according to requirements of applicable Codes there is nothing wrong in using straight CO2.

A thorough presentation and discussion of Shielding Gases for GMAW can be found at page 64 of ASM Handbook Volume 6 that is a fundamental reference book for anyone involved in welding.

See Welding Books.

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Welding Aluminum Bronze to Mild Steel [From PWL #41]

Q: - Can we weld Aluminum Bronze to Mild Steel A36? If yes what should be the electrodes?



Note: This is an actual question sent to us by one of our readers.

A: - Yes, Aluminum Bronzes are weldable to carbon steels using SMAW (Shielded Metal Arc Welding), GTAW (Gas Tungsten Arc Welding)(with Alternating Current stabilized by High Frequency) and GMAW (Gas Metal Arc Welding)(with Direct Current Electrode Positive).

One should note that aluminum in these bronzes forms tenacious oxides that must be removed before welding. This is probably the most pressing concern that should worry whoever considers to perform this welding. Shielding gas, or fluxing by electrode cover are used for preventing their formation while welding.

For the first process, electrodes ECuAl-A2 can be used with preheat from 150 to 200 0C (300 to 390 0F) for sections thicker than 6 mm (1/4").

ANSI/AWS A5.6/A5.6M:2008 Specification for Copper and Copper-Alloy Electrodes for Shielded Metal Arc Welding Edition: 9th American Welding Society, 06-Nov-2007, 38 pages Click to Order.

For the other processes above, rods or wires ERCuAl-A2 are used. For repair welding of aluminum bronze casting with highly stressed cross sections, ERCuAl-A3 may be preferred because it has less tendency to crack.

ANSI/AWS A5.7/A5.7M-2007 Specification for Copper and Copper-Alloy Bare Welding Rods and Electrodes American Welding Society, 12-Apr-2007, 32 pages Click to Order.

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Welding Titanium to Stainless Steel [From PWL #33]

Q: How is Titanium welded to Stainless Steel?

A: Titanium and Titanium alloys cannot be fusion welded to Stainless Steel. However special solid state processes that do not resort to fusion, can be used to join the two materials for preparing Transition Elements.

Among these processes are friction welding, explosive welding, ultrasonic welding, magnetic pulse welding, coextrusion or roll welding and other methods.

Regular fusion welding processes can then be used to weld each end of the transition element to the part of the same material needed to accomplish the required assembly.

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Welding Titanium Clad Steel [From PWL #23]

Q: - How is Titanium Clad Steel welded on itself?



A: - From the Article reported in Section 11 in PWL #023 we quote: "Fusion welding [the new product] is not critical to the same degree [as conventional explosively clad plate] and conventional methods of fusion welding the joints of titanium and zirconium [clad steel] plates are significantly less critical.

It has even been possible to make a welded joint by stripping back a minimum amount of titanium, fusion welding the steel substrate, covering the exposed steel with a weld deposited layer of silver and weld depositing titanium onto the silver. This gives a continuous and smooth joint profile on the titanium surface and an unbroken, continuous bond at the cladder/substrate interface."

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Welding Titanium to Cobalt base Alloy [From PWL #36]

Q: How are welds performed between Cobalt base Alloy ASTM F75 and Titanium Grade 2 and how are the joints tested? Note - The question, actually asked by one of our readers, refers to research on implants for medical applications.

A: Cobalt and Titanium cannot be successfully fusion welded to each other but they are currently joined by friction welding, provided that the shape is favorable for this type of process. Other solid state welding processes may also be suitable.

Both Cobalt and Titanium are being used for medical implants and it is reasonable to research their joint properties to exploit their specific advantages for special applications.

A recent paper dealt with "Investigations on the galvanic corrosion of multialloy total hip prostheses". An abstract can be read at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12659138&dopt=Abstract

The usual testing procedures that are used for any welding are also applicable here. In particular bend testing and tensile testing are standard. In case the joints to be tested are suspected of being brittle, they can be tested by notched bend test and by impact if required. Metallographic examination is usually conducted on sectioned, ground, polished and etched specimens.

Readers interested in Materials and Processes for Medical Devices are advised that a periodic publication of the same name is issued by ASM International and included in their renowned Advanced Materials and Processes.

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Gas Metal Arc Welding Titanium [From PWL #58]

Q - Does anyone GMA(W) weld titanium on a regular basis? It sounds good in theory but I don't remember ever seeing anything in print about Joe's Weld Shop using GMAW on some heavy titanium structure.

A: - From a quick search I found that Titanium GMAW is done but still somewhat experimentally. Special means have to be employed and the technique has to be developed.

The abstract from an article found at: DTIC,states:



"There are initiatives to develop low-cost titanium materials supplies; however, low-cost and high-rate fabrication processes are sorely lacking. Welding and joining technologies enable improved manufactured components by reducing the weight, production time, and cost of joining parts. Improved welding technology increases product lifetimes and makes possible the fabrication of large structures. Gas Metal Arc Welding (GMAW) has the potential to significantly improve the quality, speed, and penetration depth of titanium welds, while reducing the cost per part. However, this result can only be achieved if proper weld parameters are selected and dynamically maintained during the welding process due to the nature of titanium."

See also the following:

Titanium Welding Technology http://www0.nsc.co.jp/shinnihon_english/kenkyusho/contenthtml/n95/n9515.pdf

New Joining Technology for Titanium http://www.ewi.org/uploads/document_library/white_papers/WJ-May06.pdf

Pulsed GMAW of Titanium http://files.aws.org/wj/supplement/Zhang02-01.pdf

Novel Titanium Wire http://www.twi.co.uk/j32k/psg/review.xtp?id=3

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Welding Tin to Stainless Steel [From PWL #46] Note - The question was actually asked by one of our readers

Q: How do you weld tin to stainless steel?

A: You don't, due to the huge difference in melting point.If you need soldering on stainless you might pre-electroplatethe stainless with tin, possibly by duplex coating (first nickel,then tin). Finally you may solder your connection to the plated tin layer.

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Snapping Sounds from the Roof [From PWL #26]

Q: In general terms, what would cause significant popping and snapping sounds from a metal deck system over a steel joist roof system?

What corrective measures would remedy that activity? The event occurs when the roof heats up in the morning and then cools down at days' end.

A: You would hear the same sounds in a yard of empty steel barrels. As you correctly assumed it is due to heating and cooling.Consider the sheet metal surfaces emitting the snapping sounds as a membrane welded or otherwise fixed along the periphery.

When cold, the metal lays in a stable position. To simplify we will call it the concave position. Upon heating up the sheet metal tends to expand, but it is restrained mechanically, by welding or otherwise, at the borders that block its expansion.



The thermal stresses generated by heating will cause its central area, that is not limited in transversal movement, to bulge, in order to reach an equilibrium position, that we will call convex.

The situation where a mechanical system is stable with minimum internal stresses, in two different positions, is called a bi-stable equilibrium.The passage from concave to convex position occurs suddenly, upon heating, when the internal stresses are just right. The reverse movement occurs upon cooling. That is the movement generating the snapping sounds.

To avoid the snapping activity one has to permit the free thermal expansion of the sheet, by freeing at least two out of the four sides. Upon expanding freely, no stresses will build up causing the sheets to bulge and no sounds will be heard.

In order to avoid compromising stability one should provide suitable restraints in other directions while permitting free expansion and contraction along the plane of the sheet itself.

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Welding in cold Weather [From PWL #30]

Q: What is the coldest ambient temperature allowed for welding carbon steel and stainless steel pipes and structure?

A: Whenever ambient temperature causes water vapor condensation upon metals, it is recommended good practice to preheat before welding up to 120 C to make sure the joints are dry.

A few authorities, specifying the conditions for welding of Bridges and similar Structures, put the coldest ambient temperature limit, below which welding is not allowed, at 0 0F or -18 0C.See:http://www.thruway.state.ny.us/business/design-manual/appendixf.pdf(page 12) and http://www.dot.state.oh.us/testlab/StructuralSteel/Field-Welding-Inspection-Guide.pdf (page 9)

Other authorities, dealing with welding requirements for Piping and Pressure Vessels, put the coldest ambient temperature limit, below which welding is not allowed, at 32 0F or 0 0C.See: http://www.wbdg.org/ccb/NASA/NASAASC/NS15055.pdf(page 6)

For ASME Codes and Standards, the minimum temperature for welding is generally specified at 50 0F or 10 0C.

Minimum temperature and preheat requirements for welding on pressure retaining items are also referenced in the National Board Inspection Code (2004 Edition), Appendix B.

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Semi Automatic Ultrasonic Inspection [From PWL #31]

Ultrasonic Testing is a mature and robust non destructive inspection technology capable of detecting small and dangerous flaws within material bodies. As such it is widely used within the welding industry for providing safe and secure proofs of acceptable process performance meeting exacting requirements.



It is based on the properties of propagation of sound waves, of such a high frequency as to be inaudible by the human ear, and on their capacity to be reflected by geometric features or by internal imperfections.

When combined with radiographic inspection both technologies supplement each other due to their somewhat different sensitivity to specific geometric details of lack of soundness.

For all of its practical success, ultrasonic inspection has one major drawback.It is labor intensive. Moreover ultrasonic inspectors require a long formal education and preparatory apprenticeship consisting in theoretical studies covering specific chapters of acoustics, a branch of physics, and a long practical training under the supervision of experienced instructors.

Finally the trained personnel must take complex examinations and obtain a Certification demonstrating their capacity to perform successful ultrasonic inspections in order to be cleared for employment by industrial contractors, according to requirements of binding Specifications or Codes.

Various attempts are being done to automate as much as possible the ultrasonic inspection of welds in specific joint configurations. Such efforts are reported in an article published in the Issue 23 of Practical Welding Letter for July 2005. It can be read by clicking on PWL#023.

When the inspected items are repetitive and the requirements, relative to acceptance conditions, are clearly cut, some manufacturers find that it is more attractive to use equipment set up only for the specific configurations needed.

In particular this attitude is successfully applied for inspecting mechanized or robotic welds as they are performed, in line, by a welder or a helper with no specific ultrasonic training.

The body to be inspected is set-up by placing it in a well defined position relative to the sensor (called transducer), and starting the test. A mechanical scanning movement may be used if necessary.

The automatic answer or inspection result is either to accept or to reject. This is made possible by electronic manipulation of the visual signal, on a screen, representing the behavior of the ultrasonic beam.

Apart from the entrance and back peaks signaling echoes from known geometric features of the body inspected, any further peak is suspected of being caused by reflections from unwanted discontinuities.

Its intensity is measured as height from the baseline (on the screen) and its position or depth in the body is inferred from the linear relationship between the position of the reflector in the body and the horizontal distance of its signal trace from the entrance peak.

A "gate" that limits the inspected volume to the location of interest for the inspected body is superposed on the signal.

Any signal appearing in the volume of interest (that is within the gate) and of intensity higher than that of an established threshold for that specific inspection will trigger rejection.

The threshold is established by reference to ultrasonic reflections from known discontinuities of definite dimensions, introduced on purpose in special reference



test pieces.

Failed items can be then subjected to additional inspection by certified ultrasonic inspectors for further decision if needed.

Specific applications of the above principles were successfully employed also for routine examinations of critical aircraft details, where the integrity of certain components must be assured by periodic inspection.

The possible economic advantage of such a solution relative to a general ultrasonic testing performed by a certified inspector, has to be examined case by case by comparing the costs of equipment and operation.

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Thickness Range of a Plasma Cutter [From PWL #43]

Q: The capacity of a certain cutter is noted as 1 1/2" Manual and 3/4" mechanized. Why would the performance be cut in half when using a machine torch rather than a hand torch?

A: Plasma machines that can handle both manual and mechanized tasks usually have a lower thickness rating for mechanized cutting rather than manual. This is for several reasons.

Starting and ending the cut on materials close to the maximum thickness properly requires some operator technique that is easy for a human operator but difficult or impossible to program into a machine. Hence a lower rating for satisfactory cuts.

Mechanized cutting requires piercing in most cases rather than edge starts. A machine generally can not pierce successfully as thick as it can cut.

Customers using a machine in an automated set up would generally find the cut speeds on the thickest materials too slow to be acceptable for mechanized operation.

Note: This answer was supplied by B. Fernicola from ESAB, USA.

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Oxyfuel Gas Bevel Cutting [From PWL #68]

Q: In carbon steel, welding preparation of bevel with gas cutting is advisable?

A: All suitable cutting processes must be used with correct parameters for providing bevels of acceptable quality.

Depending on the amount of carbon in the steel and on the thickness, oxyfuel gas cutting can be advisable if it permits to achieve a suitable cut quality, sufficiently smooth bevel, without excessive oxidized scale or deep decarburized layer.

It is the careful balancing of all cutting variables, more than 20 according to certain counts, that help obtain a smooth edge.

In general if bevels are finish machined there is more tolerance for eventual



imperfections. Finally it is the result of further welding that helps to decide if the cut quality is acceptable or not.

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Welding Effects on Aluminum Structures [From PWL #44]

Note: The following is an actual question sent to us by a correspondent.

Q: This application is structural. It is a large (42 feet in length) box cover structure. This structure is to have 2x6x1/8 inch wall rectangular aluminum chords running the full length of the box. This 2x6 tube only seems to come in 6063-T52. This aluminum box structure also has 6061-T6 sheet for the sides and top and also 2x2x1/8 inch tubes and angles that are 6061-T6.

Problems: I cannot seem to find any allowable strength values for the 6063-T52 when it is welded - can you point me in the right direction? Also and more important is the 6063-T52 readily weldable to the 6061-T6 and is it an excellent weld as this application is structural in nature? Thank you for any help you can give me.

A: In principle welding heat will destroy the mechanical properties of heat treated aluminum alloys and revert them to those of annealed condition.

The Minimum Tensile Strength of Welded Aluminum Alloys with no post-weld heat treatment, is listed in Table 5.16 at page 232 of AWS Welding Handbook 9th Edition. For the above materials the following data are reported:

6063-T52: 17 ksi = 115 MPa6061-T6 : 24 ksi = 165 MPa

It is true that some of the properties of heat treatable alloys like 6061 and 6063 could be recovered by accurate reheat treatment if correct filler metals were employed, but this is not a feasible option for a large structure.

The welded solution is therefore applicable if the lower strength is considered adequate in design. The allowable load on the joint is established by the orientation of the heat affected zone relative to the stress direction and by its percentage relative to the whole section.

The only way out, permitting to exploit the improved mechanical properties of the above products in their as received heat treated condition, would be to implement proper mechanical joints without welding.

If it is decided to design suitable joining elements to be assembled later in the larger structure by mechanical fastening without welding, the joints themselves could be fabricated in heat treatable aluminum alloys by welding, and should be heat treated before mounting in the structure.

The last warning is that one should beware from having aluminum making contact with other materials because of the danger of galvanic corrosion, except if proper insulation materials are employed.

Welding with Robots [From PWL #48]

Q: - I have a setup of 6 Mig Welding Robots for welding Car Seats Frames. I have lots of down time because of Arc outs, changing tips. It gets worse during cold



weather. What can be done to improve?

A: - It is not uncommon for industry at large to experience breakdowns of robot lines. One way to overcome the difficulties is to grow in-house expertise of a few technicians. That is done either by sending them to follow special Mig (GMAW) courses or by hiring an instructor for the needed time.

The personnel involved should master welding expertise before starting to program robot cells because a sound theoretical background in GMAW is essential.

It is usually recommended to develop first a robust manual welding procedure for the robot parts, and then to prepare the robot program while adapting the optimized techniques used by the manual welder.

This assertion, although quite true, should be improved by making sure that the basic manual welding cycle is cautiously but firmly modified in order to exploit the robot increased productivity capabilities relative to manual processing.

In particular, while assuring quality as required, one should make skillful use of the parameters that robots can accommodate like larger wire size, higher current, higher weld speed and swift relocation between welds. Attention should be paid also to control of part distortion, minimizing spatter and establishing the most suitable sequence.

It would be a costly mistake to entrust the job of running robot cells for GMAW to personnel skilled primarily or only in robot programming. To achieve the maximum benefit from robot installations, Management should understand the special requirements of robot cells in welding environments.

Among these are parts design, part and gap tolerances, fixture design, weld process expertise and quality of the operating programs. Furthermore expert maintenance personnel should be readily available whenever needed.

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Cut Pie Welding [From PWL#054]

Q: - I have a situation where several plates are coming together at a point in the fashion of a cut pie. The plate thickness is 5/8" ABS (American Bureau of Shipping) Grade A steel. This design has all points of the pie being welded together and I know it will crystallize at the vertex, due to overheating.

Where is it noted that this design should never occur, due to the crystallization of the material at all points of intersection?

A: - The design you propose looks to me problematic, not because of crystallization (which is not a metallurgically defined defect but means other things, see further down 9.2 [in PWL#054]) but because it may be difficult to assure full weld penetration and because a triaxial state of stress (to be avoided) risks being formed in the place.

It would be better, if possible, to stop the plates short of the vertex and butt weld each plate to those on its sides, with bevels as needed, leaving a circular hole in the center of the pie, to be covered if needed by a suitable independent cover or cap.

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Fumes from Welding Zinc Coated Steel [From PWL#055]

Q: I need to know how to find the type of fumes which are created when spotwelding steel sheets with zinc coating.

A: You may have a look at

Metal Fume Fever http://files.aws.org/technical/facts/FACT-25.PDF

and at two other publications:

Resistance Spot Welding of Zinc Coated Steels http://www.spotweldequip.com/FFA%20PDF/15.pdf

Handbook for Resistance Spot Welding http://www.millerwelds.com/pdf/Resistance.pdf

Although not lethal, it seems better not to breath those fumes...

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Welder Qualification [From PWL#059]

3 - How to do it well: Welder Qualification

Q: - I have a query related to welder qualification criteria addressed as below:

Background: A welder has deposited E 7018 (F4) electrode on a 6" X Sch 40 test coupon with backing. According to QW-452.1(b), this welder is qualified to use F4 electrodes up to 14.22mm with backing. According to QW-433, this welder is also qualified to use F1, F2 & F3 with backing.

Question: If a production joint having 14.22 mm thickness with backing strip is to be deposited using E7024 (F1), E6013 (F2) & E6010 (F3) electrodes, do we have to re-qualify the above welder in all the three "F" numbers individually?

A: -

1) - 17 Jun 08 13:49 As you point out, per QW 433, F4 qualifies for F1- F4

2) - "do we have to re-qualify ...?" 17 Jun 08 14:05 No. See QW-353 in Article 2 and QW-404.15 in Article IV in the 2007 Edition of ASME B&PV Code, Section IX.

3) - 20 Jun 08 18:36 The only case in which the electrodes do NOT qualify for the lower F Number is in cases in which there is NO backing. F4 open roots qualify for F4 open roots only and F1,2,3 with backing. See QW-433

Note: The above question from a reader was submitted by us to:http://www.eng-tips.com/index.cfmwhose Contributors provided the above answers which are gratefully acknowledged.

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Threaded Hole Repair [From PWL#059]

Readers called our attention to their need to repair damaged or badly worn out threads inside holes.

While a common cure for this type of damage cannot be of general character, because each case depends on the materials involved and on the application, it is possible to hint to a few solutions that must be studied in depth to check their applicability to the prevailing service conditions.

Welding should not be considered as the first and foremost solution. On the contrary, it should be appreciated that usual fusion welding introduces much heat, with consequent development of considerable stresses and deformations.

Furthermore one should have complete knowledge on materials and condition, otherwise the part to be restored might be damaged beyond repair, so that welding should be avoided whenever possible.

Some investigation should be devoted to understand the causes of failure, which may be due to galvanic corrosion, to wear from long use or from vibration, and every effort should be applied to avoid the occurrence of the same failure again.

Apart from the obvious application of oversize bolts, which may fit oversize holes with new threads, one could possibly consider the application of HeliCoil which are commercially available Screw Thread Inserts. See: http://www.emhart.com/products/helicoil.asp

In this page on Welding FAQ, under the title: EBW Repair of a rejected Casting we reported on a case that could have some similarity with the problems addressed in this section.

Depending on application and service conditions a new threaded sleeve might be fixed in place by suitable adhesive bonding instead of EBW.

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How to Attach Nuts to a Zinc Alloy Hub [From PWL#060]

Q: I am looking to attach some hex nuts to a handwheel hub made from ASTM/ANSI DIN1743 Z410 zinc alloy. Can this material be welded? If so, what material should the nuts be and what type of rod should be used? This is a fairly low-strength application using a 3/8" hex nut being driven with an electric screwdriver. Any help?

A: Try any suitable structural adhesive. See our pages on Adhesive Bonding and on Joining Lead Tin Zinc.

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Designing a Hinge [From PWL#062]

Q - How to design a hinge for the rear of a platform dump, if running into clearance issues with the swinging part?

A - Take a clear new sheet of paper. Mark a small cross in the center. Use your



compass to draw a circle representing your hinge. Draw the fixed section of your application either at 1:1 or in scale.

On a separate transparent paper, draw the section of the rotating part at the same scale, starting from the circle that represents the hinge.

Now take the transparent paper with the drawing of the moving part and put it on the drawing of the fixed part so that the circles of the hinge match exactly. Pierce with a pin the center of the hinge of the moving part so that it can move around the pin at the hinge center.

You can now swing carefully the moving on the fixed part. Examine for eventual interferences and unwanted clearances. Modify the drawing until you are satisfied with the result, and then build it.

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Welding High Tensile Bolts [From PWL#063]

Q: I am trying to find out if you loose tensile strength of threaded rod/bolts if you weld them end to end (to gain extra length)? The rod is high tensile steel.Also what sort of weld should be carried out?

A: Don't weld high strength bolts. As you suspect you will loose strength. Welding heats the material and destroys the mechanical properties obtained through heat treatment.

There is no suitable welding method that will preserve strength. If welding is performed however, depending on the type of steel, the mechanical properties could be partly restored only by repeating completely the original heat treatment.

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Cutting Pipes and MPI [from PWL#065]

Q: Should one perform Magnetic Particles Inspection before welding, after cutting pipes by any abrasive process?

A: The use of abrasive discs for cutting pipes (or any other item)(but not abrasive waterjet cutting) can heat the edges to quite high a temperature, unless cooling water is used to flood the place.

While mild steel will not harden (and will not crack) upon being heated by abrasive cutting even if not cooled, alloy steels subjected to uncontrolled heating can crack because of self quenching that generates untempered martensite.

Therefore, for materials susceptible to cracking, the absence of cracks due to this process should be controlled by MPI if quality production has to be assured.

Even if this requirement is not spelled out by applicable codes, it would be a matter of good workmanship to establish safe practices for the process and/or conservative measures for inspection.

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[From PWL#067, Section 3]

Q: Writing M.Sc Thesis for SAAB Automobile AB in Sweden. Looking into a sandwich material called Hybrix to see if it can be used in an automobile body.

The sandwich material I'm investigating is made from thin facesheets (0.1 mm thick) of austenitic stainless steel. Arc weld studs are seemingly impossible to weld to this sandwich material due to the thin facesheets.

My question to you: are there any alternatives for welded studs? Maybe something that is more like a rivet or bolt.

PWL Note: I am glad of this opportunity to introduce to my readers a new material possibly not yet widely known. See the brochure:http://www.lamera.se/eng/images/stories/pdf/lamerabrochure07_lores.pdf

A: You could try to use through passing rivets or bolts as per sheet Tips for Processing.

But how will the joints behave under load? Probably adhesive bonding, also mentioned in the above sheet, is likely to be more suitable, as it is used in aircraft and in car manufacturing. Even Laser welding is proposed there for joining, although without details.

I see that data on Bending Stiffness against Surface Density are reported, more important for crashworthiness properties than classic tensile testing data.

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What Tungsten is used for Titanium Tig? [From PWL#071, Section 3]

As it is widely known, available tungsten electrodes used in Gas Tungsten Arc (or Tig) Welding can be made of a few different types of powder metal compacts.

For Titanium welding the conventional thoriated Tungsten electrodes known as EWTh-1 and EWTh-2 are used (with 1 or 2%Thorium respectively), ground to a point.

Welding-titanium is done with straight polarity direct current (tungsten electrode connected to the negative pole).

See also Welding Titanium.

Welding Lead [From PWL#073, Section 3]

The following comment was sent by Mr. Timothy Lynch President of Kenneth Lynch & Sons from the United States.

Date: 12 Aug 2009

Sir: I read with interest your treatise on welding lead. Well done, except that we use oxygen and hydrogen mix to weld lead (statuary).

The reason is that oxy-acetylene will cause the lead puddle to "pop" or blow out,



sometimes causing burns if the spatter lands on your skin.

This never occurs with oxy-hydrogen mix. All other problems remain as described.

s/ Tim Lynch

(The reference is to my page on Joining Lead Tin Zinc).

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Brazing Flux Removal [From PWL#075, Section3]

Q - Ran into an horrendous problem removing brazing flux - is there a process that would reduce the level of aggravation and labor? The metals involved were German silver and a stainless that is extremely tough. The object was to braze a guard to the blade.

A - You probably used a flame for brazing. Overheating should be avoided. In general flux removal should be done immediately after brazing, and the method used is generally hot water rinsing, possibly with soft brushing.

Immersing the brazed joint in water before full cooling, helps flux removal, if not objectionable for other reasons. Leaving the flux on, causes it to oxidize making it a form of glass, more difficult to remove.

Pickling solutions or chemical cleaning is available. Mechanical means are a possibility, including fiber brushing, wire brushing, blast cleaning and steam jet. Next time you may consider using a suitable stop off, to limit the area where flux is spread, heating as low as possible and removing flux immediately.

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Selecting Carbide for Hardfacing [From PWL#077]

Q: We use Tungsten Carbide to hard face our steel and I recently heard from someone that Vanadium Carbide cost 30% less, you get 30% more coverage per pound. Is there any truth to this and if so is the abrasion resistance as good as tungsten carbide. Any info you have would help us a lot. Thanks.

A: While it is essentially a good thing to try to improve processes and reduce expenses, one has to be very cautious before changing processes working satisfactorily. In particular one has to be extremely skeptic when someone (not better defined, could have hidden interests?) throws in an idea whose reckless adoption might cause much damage.

There is more to Hardfacing than the carbide powder used. The abrasion resistance of the final application depends much on the type of thermal spray process, on actual spraying parameters, on hardness but also on adhesion and on the type of materials your equipment is called to work on.

Tungsten carbide is called the ultimate in abrasion resistant qualities. If you are interested in comparing two different carbide powders, you should set up an experimental study for your specific applications and draw conclusions from practical results.



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Braze-Welding of Steel [From PWL#078]

Q: We have to complete various tests on "coupons" fitted together. On 2 pieces of very thin 1/16" metal, I sheared them off at 8 inch lengths (3" wide) and went into the grinding room and ground everything that the braze-weld would touch. I tacked both outer sides (which looked excellent) and then proceeded to braze-weld. I had a thin layer of bronze on the top side, no penetration and then after 6 inches the whole length of the weld cracked right down the middle of the weld.

A: The above description does not mention essential steps of the process. Both sides of the joint should be generously covered with flux before even starting to braze-weld. The groove gap between the parallel coupons should be between 1/32 and 1/16". The oxyacetylene flame should be slightly oxidizing as explained in the following ESAB Handbook-Braze Welding page at http://www.esabna.com/euweb/oxy_handbook/589oxy14_1.htm and then use the right arrow to see the following pages.

Finding the right base metal temperature for successful wetting (ESAB calls this "tinning") of the base metal by the brass filler metal may be the most tricky part of the exercise. They suggest to try a bead on plate for getting the feeling.

To obtain penetration of the filler metal in the joint one should have the bottom side of the joint reachable by the flame, and then alternatively manipulate the torch from both sides without overheating the base metal.

Trying to do this again and again is the only way to reach the needed skill.

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Inside Tube Inspection [from PWL#082 - Section 3]

Q: How can I perform visual inspection of welds or corrosion condition from the inside of tubes or small containers with no direct line-of-sight access?

A: You should procure long and thin optical instruments called Borescopes. There are many types, portable, rigid or flexible if made with optical fibers, and they contain an autonomous light source to illuminate the area to be inspected. Sophisticate equipment may include a camera and transmit the view to a portable TV screen.

There use is invaluable but the inspector needs to get training and some experience before being able to perform reliable inspections.

Interested readers can browse manufacturers' catalogs to find the instrument best adapted to their requirements.

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Safety in Hydrogen Furnaces [from PWL#083 - Section 3]

The Hydrogen protective atmosphere has many useful applications in furnaces for metal processing, because of the reducing properties of this light gas. It is



therefore widely used for bright annealing processes and for brazing stainless steels and nickel alloys.

However it has a number of safety issues because Hydrogen gas at 1 atm is flammable in the concentration range 4–74% (volume per cent of hydrogen in air) and is explosive in the concentration range 18.3–59% (volume per cent of hydrogen in air).

Therefore precise procedures must be followed when starting up and when shutting down, because it is in those transition periods that air may find a way to enter the furnace and form an explosive mixture with hydrogen.

Security alarms and features should inhibit the start of any operation if the gases are low in volume and/or pressure in their respective containers, or if any of the valves is found faulty.Leaks from the Hydrogen line are particularly dangerous and therefore frequent checks should verify their complete absence. Hydrogen sensors must be used for rapid detection of hydrogen leaks.

The air present in the furnace space must be removed before admitting Hydrogen gas. That is done by purging the furnace with an inert gas, usually nitrogen. Depending on the furnace build and function (batch type or continuous) a slight overpressure will always be maintained to avoid air leaking in.

Hydrogen excess and that portion expanding due to heat, will be vented at the highest point and lit with a pilot flame to burn quietly in air (producing drops of water).

Also at shut down, the inert gas is admitted to displace Hydrogen, heat is removed and the furnace is let cool down. Only then doors are opened and air is admitted, to unload the treated parts.

The security issues to take care of are non programmed black out occurrences (interruption of electricity flow), interruption of cooling water flow, if used to cool down gaskets and doors, interruption of Hydrogen gas supply or sudden loss of availability of purge inert gas. A spare inert gas container must be easily accessible and operational with a few valve manipulations.

For each of these emergencies it is imperative that automatic shut down procedures step in without manual intervention and overtake any other standard operation. The automatic planned shut down must include positive electric power interruption, positive hydrogen flow interruption, and admission of inert gas through a normally open valve (that opens when power goes off).

As accidental explosions may be extremely dangerous, one should have in place back up systems, a thorough maintenance plan of periodic equipment tests, and a good training program frequently rehearsed.

If properly planned, executed, maintained and controlled, hydrogen furnaces are not any more dangerous than other industrial equipment and can provide essential contribution to production facilities.

See: Hydrogen Safety http://www.hydrogen.energy.gov/pdfs/doe_h2_safety.pdf

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Disposing of Arc Strikes



[from PWL#084 - Section 3]

Arc Strike is a surface discontinuity caused by a localized application of an electric arc. It appears as remelted or heat affected material or as a surface change. During welding it may be caused by arc initiation not exactly where the weld puddle is formed.

Depending on the material and the application, the blemishes appearing on the spot need to be cleaned and removed because they include remelt material, hard spots and possibly cracks. In case of low carbon steel it will be enough to grind out the surface lightly to remove the apparent discontinuity.

For medium or high carbon steel, removal of the heat affected zone is required by grinding to some depth, to be sure that no spots with untempered martensite will remain near the affected surface.

An interesting point was clarified by Damian J. Kotecki in his Stainless Q&A note published at page 14 in the July 2010 issue of the Welding Journal. There the reference is to the Duplex Stainless Steel type 2205 which is not hardenable.

Answering to a concerned reader who was annoyed by the insistence of an inspector who requested the removal of the complete heat affected zone, Mr. Kotecki justified the inspector's request explaining that in the said material arc strikes generate locally almost 100% ferrite in the HAZ.

By a complex chain of events, the nitrogen (austenite former) which has no time to reach the austenite and diffuse there, precipitates as chromium nitrides in the large ferrite grains. Therefore the ferrite grains remain depleted of chrome and prone to corrosion.

Interested readers are urged to see the original note. In conclusion arc strikes should be avoided but, if present, they should be thoroughly removed.

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Change of Material [from PWL#085 - Section 3]

A very interesting note was published on page 18 of The Welding Journal for August 2010. A reader reported on a high leak rate found in manually brazed distribution systems and asked for possible causes. Originally the systems were made of copper tubing. Recently however, in order to save on material costs, a switch had been made in some systems, substituting copper plated steel tubing for copper tubing.

In his very detailed and reasoned answer, Tim P. Hirthe, the brazing expert, while conceding that the material substitution could have been a good idea, warns on the differences in thermal conductivities, that could cause steel tubes to overheat. In that case the copper coating could become readily damaged or removed, compromising the brazing application.

Additional warnings concern the presence of phosphorus in certain silver base brazing filler metals, intended to deoxidize the copper surface, but producing brittle compounds if let to alloy with iron, and also the difference in Coefficient of Thermal Expansion (CTE)(between copper and steel) making it quite difficult to maintain a suitable clearance between elements at brazing temperature.

The problem is multiplied by having a team of 15 persons performing manual brazing, difficult to train for the special requirements and difficult to supervise. A



possible substitution of filler metal is proposed, one suitable for larger than usual clearances.

Summing up, the brazing expert, considering the stricter brazing procedures changes that should be made and the increased risks of failure, asks if it would not be more cost effective after all to stick with the old material.

While it is true that no progress would be possible if old procedures were never questioned, looking only for savings at the material level without taking into account possible process implications, risks to procure more damage than benefit.

Interested readers are urged to seek the original publication, whose details are described above.

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Proper Water Cooling of Spot Welding Electrodes [from PWL#087 - Section 3]

Practical notes are often most useful in that they address common problems. I usually pay attention to the Q&A appearing in the Welding Journal because there is frequently something to learn. In the November 2010 issue at page 16 there is an explanation on the importance of the correct mounting of water tubes in resistance welding electrodes.

The adjustable tube extensions should be so mounted, by sliding them on their support as necessary, that they reach the bottom of the electrode internal cavity. The tube end should be cut at 45 degrees to make sure that water flows unhindered without forming steam pockets.

Cooling water should be circulated as near as possible to the tip to be effective in reducing the copper temperature, to keep its strength as needed during the forging cycle when large pressures are applied.

Keeping electrodes cool prevents copper softening and tip mushrooming, maximizing electrodes life and improving spot weld quality. Either sliding or spring loaded tubes are used. When becoming distorted or otherwise damaged they must be substituted with new ones and regularly maintained.

The note recommends to use straight electrodes whenever possible. If not, offset tip holders with straight tips should be preferred. To further enhance the importance of the subject, the author of the note, Tim Snow, refers readers to a research paper titled "Influence of Water Temperature and Flow on Electrode Life" available at www.unitrol-electronics.com from the Download section.

Interested readers are urged to seek the original article from the source mentioned above.

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Increasing the Weld Deposition Rate [From PWL#088 - Section 3]

Weld Deposition Rate directly affects the productivity of the operation. Therefore it should be considered as one of the most important factors for satisfactory financial results.



For the processes employing continuous wire as filler metal, like Gas Metal Arc Welding (GMAW or Mig), Flux Cored Arc Welding (FCAW) and Submerged Arc Welding (SAW), there is an easy way to increase the Deposition Rate, with minimum adjustment of parameters.

One recommended but under-used way of increasing the Weld Deposition Rate without incurring in unacceptable defects like burn through, is to increase the Electrode Extension called also Wire Stick Out (WSO), representing the free length of wire between the contact tip and the arc.

The reasons underlying the dramatic change in performance produced by this simple change are explained in some detail in the article in section 11 in Issue 88 of Practical Welding Letter for December 2010. Click on PWL#088 to see it.

That note refers in particular to SAW, but the principles are applicable also for the other mentioned processes.

Slight adjustments may be needed for other parameters, in particular the voltage may need a small increase to make up for the additional voltage drop along the added length of electrode consequent to the increased electrode extension.

Increased deposition rate, due to the higher resistance heating of the electrode between the contact tip and the arc, is the main advantage. Other advantages include lower heat input, higher impact properties, narrower heat affected zone, decreased penetration and lower dilution levels.

If burn through was a problem before increasing the extension, it may well be solved with this technique. It is true that some experimentation is needed to find the best set of parameters but understanding the basics should improve the performance.

In any case it should be one of the first changes to be attempted when working on improving the productivity of any welding operation, large or small.

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Find if an aluminum alloy is weldable or not [From PWL#089 Section 3]

Good that you asked. It is better to pause and to inquire to get the answer before welding, otherwise one may make irreversible damage to whatever was incautiously welded.

Weldable is to be understood by fusion welding, that is by processes that use an electric arc or a flame to cause melting of the alloy.

Aluminum alloys are also classified as being or not Heat Treatable by Solutioning and Precipitation Hardening. For those alloys that are both heat treatable and weldable like 6061 and similar alloys, additional heat treatment may be needed to restore mechanical properties after welding.

Heat treatable high strength aluminum alloys like 2024 and 7075 which are not successfully welded by fusion welding, are currently welded by resistance spot welding.

One should know which is the material one wants to weld. In case the material is new and identified by a standard designation, it is easy to find in handbooks or from



the supplier its welding characteristics.

If you consider repairing an aluminum object whose designation you ignore, first look on it to see if it shows signs of original welding. If it was welded it is weldable. If it has only spot or seam resistance welds, it is probably not fusion weldable.

If the original material is not known, the family to which it belongs should be determined at least by qualitative analysis, preferably by X-ray fluorescence methods. See Material Identification.

Hardness testing should also be performed to determine the material condition.

See also:Aluminum Welding and Welding Aluminum, Reprint from HIWT

Please be advised that special aluminum alloys, called Metal Matrix Composites, including reinforcing particles of various types are not considered weldable by common means. See Joining Aluminum MMC.

Also a different class of aluminum base materials for moderately elevated temperatures, called Dispersion Strengthened Aluminum Alloys and introduced further down in Section 7 in this issue of PWL, are not considered weldable unless special procedures are developed and applied. To the same subjects are devoted the links presented in the Mid Month Bulletin, the section appended at the end of PWL#089.

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Welding Unknown Materials [From PWL#091 - Sect. 3]

Q: I am attempting to tig weld together two apparently dissimilar aluminum alloys. Also, one of them has a 3mm wall thickness and the other one a 10mm thickness. Neither piece is cast, but both are billet machined. I cannot start an arc pool on the thicker material, do I need to preheat the part, and how do I avoid oxidation during the pre-heating process? I am worried about using higher current flows because I do not want to destroy the more delicate piece.

A: Why would not you try the right way to do welding? You have unknown materials. Please identify them. Only then, once you know what materials they really are, can you look for a suitable welding method. See my page: http://www.welding-advisers.com/Material-identification.html

I recommend that you try to locate a source of x-ray fluorescence analysis (qualitative) and that you request also hardness test for both parts.

P.S. - It is known and should be always remembered that certain aluminum alloys are not fusion weldable, although they may be welded by resistance welding or by other methods. Typical examples are the alloys 2024 and 7075 that should never be fusion welded. See Aluminum Welding.



Hard Facing of Austenitic Manganese Steel [From PWL#092 - Section 3]

Austenitic Manganese Steel contains 1-1.4 %C and 10-14 %Mn. This composition stabilizes the austenitic structure that is maintained even upon rapid quenching from high temperature. However, upon reheating to a moderate temperature, the material is embrittled by a partial transformation of austenite.

Manganese steel, obtainable in cast or wrought form, is a low-strength, high-ductility material. This material is tough and wear resistant, with the capability to work-harden from an initial hardness of 240 BHN (Brinell Hardness Number) (23 Rc = Rockwell C) to well over 500 BHN (51 Rc).

Work hardening occurs naturally as this steel is subjected to impact conditions under normal work in demanding applications such as primary rock crushing. This process increases the hardness of the affected metal and its abrasion resistance. If cracking of the work hardened layer occurs, crack propagation is quickly arrested and prevented by the tougher original (not work hardened) core.

As this material is selected primarily for impact and wear resistance, it is not uncommon that working surfaces of various implements wear out in time to the point where rebuilding become imperative. This is normally achieved by hard facing using arc welding to deposit new wear resistant layers.

To avoid the embrittlement of the base metal, welding and hard facing require procedures that result in minimum heat buildup. Severely worn or cracked material is first removed and replaced by welding using electrodes of austenitic manganese steel. Small parallel stringer beads are usually recommended, with thorough cooling between them. When much material must be added, round or square section bars of austenitic manganese steel can be embedded within the welded build up material.

Heat building should be minimized by skip welding, or moving from a weld area to another one relatively far away, before coming back to continue welding in the previous place. The same procedure is followed when applying, on the top, wear resistant alloys. A huge selection of materials is available, to be selected with the help of experts or manufacturers and according to previous experience.

In all welding operations base metal temperature should not exceed 260 0C (500 0F). Limiting the temperature reduces metal shrinkage, stress buildup, distortion and surface cracking of deposits. Preferably two or more hard facing layers are applied to minimize dilution effects of base material on the working surfaces.

Accurate bookkeeping of time to wear out and of costs both for the original implements and for repairs can help in improving the economic performance and in maintaining tools and assemblies in working condition.

Stress Relieving Test [From PWL#093 - Section 3]

Recent queries addressed stress relieving test. As the specific conditions referring to the cases confronting the inquirers are not known in any details, the answer here refers to general cases.

There is no practical mechanical test capable to determine, by measuring a given property (like hardness), if the process was applied or not. Therefore in case of doubt if the process was applied or not, the only resort would be to make it again.



Whenever stress relieving procedures (see Stress Relieving) are specified in engineering requirements, there must be an established record keeping method that certifies for every workpiece submitted to this procedure, that the process was indeed done as prescribed.

The record, normally written and signed by an authorized inspector, must define the item, by serial number if necessary, the facility used, the parameters (date, time, temperature), the operator, and include furnace graphs if available. Special remarks like interruptions, must also be included.

As sometimes stress relieving operations may cause deformations, dimensional checks should be performed to make sure that the items are still acceptable. Normally hardness test are not required except in special cases.

If stress analysis is required for development programs, it is not generally a routine inspection, and will be performed on experimental basis.

Steel parts undergoing stress relieving at elevated temperature may develop a surface scale that should be removed before applying paint, by such a process as specified in engineering drawings. See Abrasive Blast Cleaning.

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