Steel Make Up

8/9/2019 Steel Make Up

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Steel Make-Upteel Make-UpDr. Eng. Hamed A. NagyDr. Eng. Hamed A. Nagy


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Dr. Eng. Hamed A. NagyWeld- Inspecta Co.

INSPECTAIntroductoryntroductory Mechanical properties of a metal can beMechanical properties of a metal can be

altered by the application of variousaltered by the application of various

mechanical and thermal treatments.mechanical and thermal treatments. Drastic changes will also occur if theDrastic changes will also occur if the

chemical composition is changed.chemical composition is changed.

Also, chemical composition will also haveAlso, chemical composition will also havean effect on its corrosion resistance andan effect on its corrosion resistance and

weldability.weldability.


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INSPECTABasic MetalBasic Metal

StructuresStructures

Atoms are so small that they cannot be seen,Atoms are so small that they cannot be seen,

even with the most powerful microscopes.even with the most powerful microscopes.

At certain temperature ranges, they tend toAt certain temperature ranges, they tend toform substances having specific shapes.form substances having specific shapes.

This is because there are definite forces actingThis is because there are definite forces acting

between these individual atoms These forcesbetween these individual atoms These forces

are in equilibrium.are in equilibrium.


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StructuresStructures 'Home' positions.'Home' positions.

Interatomic Spacing.Interatomic Spacing.

Below a metal's yield point, Elastic,Below a metal's yield point, Elastic,WHY?WHY?

It was noted before that the metal atomsIt was noted before that the metal atoms

exhibit a very specific spacing at a givenexhibit a very specific spacing at a giventemperature, or internal energy.temperature, or internal energy.

Expansion?Expansion?


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StructuresStructures Liquid metal has a higher internal energyLiquid metal has a higher internal energy

with greater interatomic spacing, and iswith greater interatomic spacing, and is

considered to be amorphous.considered to be amorphous. There are several ways of reducing orThere are several ways of reducing or

eliminating residual stresses.eliminating residual stresses.

Stress relief.Stress relief. Vibration.Vibration.


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INSPECTACrystal StructuresCry

stal Structures

In a solid metal, the atoms tend to alignIn a solid metal, the atoms tend to align

themselves into orderly lines, rows, and layersthemselves into orderly lines, rows, and layers

to form three dimensional crystalline structures.to form three dimensional crystalline structures. "Unit cell"."Unit cell".

Body-centered cubic (BCC),Body-centered cubic (BCC),

Face-centered cubic (FCC),Face-centered cubic (FCC),

Body centered tetragonal (BCT), andBody centered tetragonal (BCT), and

Hexagonal close-packed, (HCP).Hexagonal close-packed, (HCP).


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INSPECTASolidification of MetalsSolidification of Metals

Nuclei.Nuclei.

Then Grain.Then Grain.

Mechanical properties can be dependentMechanical properties can be dependent

upon the grain size of the metal.upon the grain size of the metal.

Effect varies with temperature.Effect varies with temperature.


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INSPECTAAlloyingAlloying

The properties of metallic elements can beThe properties of metallic elements can be

altered by the addition of other elements, whichaltered by the addition of other elements, which

may or may not be metallic.may or may not be metallic. Alloying elements are included in the baseAlloying elements are included in the base

metal lattice (the general arrangement ofmetal lattice (the general arrangement of

individual atoms) in various ways dependingindividual atoms) in various ways depending

upon the relative sizes of the atoms.upon the relative sizes of the atoms. Smaller atoms, such as carbon, nitrogen andSmaller atoms, such as carbon, nitrogen and

hydrogen, tend to occupy sites be interstitial.hydrogen, tend to occupy sites be interstitial.


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INSPECTAAlloyingAlloying

Alloying elements with atoms close to the sizeAlloying elements with atoms close to the sizeof those of the base metal tend to occupyof those of the base metal tend to occupysubstitutional sites.substitutional sites.

Nearly all engineering metals are alloysNearly all engineering metals are alloysconsisting of one major element and variableconsisting of one major element and variableamounts of one or more additional elements.amounts of one or more additional elements.Alloys usually consist of many randomlyAlloys usually consist of many randomly

oriented grains with each grain arranged in aoriented grains with each grain arranged in aspecific way and containing one or more of thespecific way and containing one or more of thecharacteristic phases that exist for the alloy.characteristic phases that exist for the alloy.


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INSPECTAMicrostructuralMicrostructural

Constituents ofConstituents of

Carbon SteelCarbon Steel The overall arrangement of grains, grainThe overall arrangement of grains, grain

boundaries, and phases present in a metallicboundaries, and phases present in a metallicalloy is called its microstructure.alloy is called its microstructure.

This microstructure is affected by theThis microstructure is affected by thecomposition or alloy content, and by othercomposition or alloy content, and by otherfactors such as forming and heat treatingfactors such as forming and heat treatingoperationsoperations

Iron and steels undergo changes in theirIron and steels undergo changes in theircrystallographic arrangement as a result ofcrystallographic arrangement as a result oftemperature changes.temperature changes.


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Carbon SteelCarbon Steel This allows us to change the mechanicalThis allows us to change the mechanical

properties of a specific alloy through heproperties of a specific alloy through he

application of various heat treatments.application of various heat treatments. "Iron-Carbon Phase Diagram""Iron-Carbon Phase Diagram"

Ferrite,Ferrite,

Austenite,Austenite,

CementiteCementite


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Carbon SteelCarbon Steel Hypoeutectoid, eutectoid and hypereutectoidHypoeutectoid, eutectoid and hypereutectoid

typestypes

At 723 C, the horizontal line representingAt 723 C, the horizontal line representingtransformation temperature is referred to as thetransformation temperature is referred to as the

AC1AC1

Transformation will occur over a range ofTransformation will occur over a range of

temperatures with complete transformationtemperatures with complete transformationoccurring only when the temperature is raisedoccurring only when the temperature is raised

above the sloping line designated as the A3.above the sloping line designated as the A3.


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Carbon SteelCarbon Steel Pearlite can only occur when sufficient time isPearlite can only occur when sufficient time is

allowed for the atoms to diffuse into thatallowed for the atoms to diffuse into that

arrangement.arrangement. Diffusion is simply the migration of the atomsDiffusion is simply the migration of the atoms

within the solid metal structure.within the solid metal structure.

When the cooling from the austenitic rangeWhen the cooling from the austenitic range

occurs more rapidly, there are significantoccurs more rapidly, there are significantchanges in this transformation for a given steelchanges in this transformation for a given steel

alloy.alloy.


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Carbon SteelCarbon Steel Upon rapid cooling, principal microstructuresUpon rapid cooling, principal microstructures

produced include fine pearlite, bainite andproduced include fine pearlite, bainite and

martensite.martensite. However, martensite has characteristically theHowever, martensite has characteristically the

low ductility and toughness.low ductility and toughness.

To improve the ductility and toughness withoutTo improve the ductility and toughness without

significantly decreasing the hardness andsignificantly decreasing the hardness andtensile strength of the martensite, a processtensile strength of the martensite, a process

referred to as tempering is employed.referred to as tempering is employed.


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INSPECTAHeat TreatmentsHeat Treatments

The basic heat treatments include annealing,The basic heat treatments include annealing,

normalizing, quenching, tempering, preheat,normalizing, quenching, tempering, preheat,

post heat and thermal stress relief.post heat and thermal stress relief.

Annealing is a softening treatment used toAnnealing is a softening treatment used to

increase the metal's ductility at the expense ofincrease the metal's ductility at the expense of

its strength.its strength.

Metal is raised just into the austenitic range,Metal is raised just into the austenitic range,


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held for one our per inch of thickness orheld for one our per inch of thickness or

a minimum of one hour,a minimum of one hour,

and then cooled very slowly.and then cooled very slowly. Normalizing also softens the metal, butNormalizing also softens the metal, but

not as significantly as annealing.not as significantly as annealing.

The only difference is cooling in still air.The only difference is cooling in still air.


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Quenching differs from annealing andQuenching differs from annealing andnormalizing in that the resulting mechanicalnormalizing in that the resulting mechanicalproperties show significantly increasedproperties show significantly increased

hardness and strength and decreased ductility.hardness and strength and decreased ductility. By immersing the part in a quenching medium,By immersing the part in a quenching medium,

such as water, oil or brine (salt water).such as water, oil or brine (salt water).

To improve the ductility without significantTo improve the ductility without significantdegradation of the metal's strengthdegradation of the metal's strengthcharacteristics, a tempering treatment ischaracteristics, a tempering treatment isusually performed.usually performed.


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Reheated to a temperature below theReheated to a temperature below the

lower transformation temperature,lower transformation temperature,

held for a short time to allow the highlyheld for a short time to allow the highlystressed martensitic structure to relaxstressed martensitic structure to relax

somewhat, and then cooled.somewhat, and then cooled.

Preheat treatments.Preheat treatments. Thermal stress relief,Thermal stress relief,


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INSPECTADiffusionDiffusion

Atoms in the liquid state can move aboutAtoms in the liquid state can move about

easily with respect to each other;easily with respect to each other;

Increases with temperature.Increases with temperature. Major examples, HydrogenMajor examples, Hydrogen

Embrittlement and Sensitization.Embrittlement and Sensitization.


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INSPECTAAlloy GroupsAlloy Groups

Steels can be divided into three subcategories: plainSteels can be divided into three subcategories: plaincarbon steels, low-alloy steels, and high alloy steels.carbon steels, low-alloy steels, and high alloy steels.

Based on tonnage, plain carbon steels are the mostBased on tonnage, plain carbon steels are the most

widely used.widely used. They contain primarily iron but also small additions ofThey contain primarily iron but also small additions of

carbon, manganese, phosphorus, sulfur and silicon.carbon, manganese, phosphorus, sulfur and silicon.

Compositions of some of stainless steel types, whichCompositions of some of stainless steel types, whichare divided into five groups, austenitic, martensitic,are divided into five groups, austenitic, martensitic,ferrite, precipitation hardening, and the duplex grades.ferrite, precipitation hardening, and the duplex grades.


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INSPECTAAlloying Elements-Alloying Elements-

CarbonCarbon

is generally considered to be the mostis generally considered to be the most

important alloying element in steel (up toimportant alloying element in steel (up to

2%)2%) Most welded steels have less than 0.5%.Most welded steels have less than 0.5%.

Carbon can exist either dissolved in theCarbon can exist either dissolved in the

iron, or in a combined form such as ironiron, or in a combined form such as ironcarbide (Fe3C).carbide (Fe3C).


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INSPECTACarbonCarbon

Increased amounts of carbon increaseIncreased amounts of carbon increase

hardness and tensile strength, as well ashardness and tensile strength, as well as

response to heat treatment (hardenresponse to heat treatment (hardenability).ability).

On the other hand increased amounts ofOn the other hand increased amounts of

carbon reduce weldability.carbon reduce weldability.


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INSPECTASulfurSulfur

Is usually an undesirable impurity in steelIs usually an undesirable impurity in steel

rather than an alloying element. In amountsrather than an alloying element. In amounts

exceeding 0.05% it tends to cause brittlenessexceeding 0.05% it tends to cause brittleness

and reduce weldability. Alloying additions ofand reduce weldability. Alloying additions of

sulfur in amounts from 0.10 to 0.30% will tendsulfur in amounts from 0.10 to 0.30% will tend

to improve the machinability of a steel.to improve the machinability of a steel.

Such types may be referred to as "resulfurized"Such types may be referred to as "resulfurized"or "free-machining". (not intended for useor "free-machining". (not intended for use

where welding is required).where welding is required).


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INSPECTASiliconSilicon

Usually only small amounts (0.20%) areUsually only small amounts (0.20%) arepresent in rolled steel when it is used as apresent in rolled steel when it is used as adeoxidizer.deoxidizer.

In steel castings, 0.35 to 1.00% is commonlyIn steel castings, 0.35 to 1.00% is commonlypresent.present.

Silicon dissolves in iron and tends toSilicon dissolves in iron and tends tostrengthen it.strengthen it.

Weld metal usually contains approximatelyWeld metal usually contains approximately0.50% silicon as a deoxidizer.0.50% silicon as a deoxidizer.


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INSPECTASiliconSilicon

Some filler metals may contain up to 1% toSome filler metals may contain up to 1% to

provide enhanced cleaning the deoxidation forprovide enhanced cleaning the deoxidation for

welding on contaminated surfaces.welding on contaminated surfaces.

When these filler metals are used for weldingWhen these filler metals are used for welding

of clean surfaces, the resulting weld metalof clean surfaces, the resulting weld metal

strength will be markedly increased:strength will be markedly increased:

The resulting decrease in ductility couldThe resulting decrease in ductility couldpresent cracking problems in some situations.present cracking problems in some situations.


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INSPECTAChromiumChromium

is a powerful alloying element in steel.is a powerful alloying element in steel.

It is added for two principle reasons; first, itIt is added for two principle reasons; first, itstrongly increase the hardenability of steel, andstrongly increase the hardenability of steel, andsecond, it markedly improves the corrosionsecond, it markedly improves the corrosionresistance of alloys in oxidizing media.resistance of alloys in oxidizing media.

But could cause excessive hardness andBut could cause excessive hardness andcracking in, and adjacent to the weld.cracking in, and adjacent to the weld.

Stainless steels contain chromium in amountsStainless steels contain chromium in amountsexceeding 12%.exceeding 12%.


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INSPECTAMolybdenumMolybdenum

This element is a strong carbide former and isThis element is a strong carbide former and is

usually present in alloy steels in amounts lessusually present in alloy steels in amounts lessthan 1.0%.than 1.0%.

it is added to increase hardenability andit is added to increase hardenability and

elevated temperature strength.elevated temperature strength.

It is added to the austenitic stainless steels toIt is added to the austenitic stainless steels to

improve pitting corrosion resistance.improve pitting corrosion resistance.


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INSPECTANickelNickel

GreatGreat

is added to steels to increase theiris added to steels to increase theirhardenability.hardenability.

It performs well in this function because it oftenIt performs well in this function because it oftenimproves the toughness and ductility of theimproves the toughness and ductility of thesteel, even with the increased strength andsteel, even with the increased strength andhardness.hardness.

Nickel is frequently used to improve a steel'sNickel is frequently used to improve a steel'stoughness at low temperatures.toughness at low temperatures.


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INSPECTAAluminumAluminum

Is added to steel in very small amountsIs added to steel in very small amounts

as a deoxidizer.as a deoxidizer.

It is also a grain refiner for improvedIt is also a grain refiner for improvedtoughness; steels with moderatetoughness; steels with moderate

aluminum additions are referred to asaluminum additions are referred to as

having been made to a 'fine grainhaving been made to a 'fine grainpractice'.practice'.


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INSPECTAVanadiumVanadium

Increases the hardenability of a steel.Increases the hardenability of a steel.

In amounts greater than 0.05%, thereIn amounts greater than 0.05%, there

may be a tendency for the steel tomay be a tendency for the steel tobecome embitter during thermal stressbecome embitter during thermal stress

relief treatments.relief treatments.


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INSPECTANiobium (ColumbiumNiobium (Columbium((

like vanadium, is generally considered tolike vanadium, is generally considered to

increase the hardenability of a steel. However,increase the hardenability of a steel. However,due to its strong affinity for carbon, it maydue to its strong affinity for carbon, it may

combine with carbon in the steel to result in ancombine with carbon in the steel to result in an

overall decrease in hardenability.overall decrease in hardenability.

It is added to austenitic stainless steels as aIt is added to austenitic stainless steels as astabilizer to improve as-welded properties.stabilizer to improve as-welded properties.


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INSPECTADissolved GasesDissolved Gases

Hydrogen, oxygen, and nitrogenHydrogen, oxygen, and nitrogen

All dissolve in molten steel and can embrittleAll dissolve in molten steel and can embrittle

steel if not removed.steel if not removed. Steel refining processes are designed toSteel refining processes are designed to

eliminate as much of these gases as possible.eliminate as much of these gases as possible.

Special fluxes or shielding gases are used toSpecial fluxes or shielding gases are used to

prevent their solution in the molten weld metal.prevent their solution in the molten weld metal.


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INSPECTAIron-Carbon Diagramron-Carbon Diagram

%C

Tempe

ratu

re


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D E H d A NWeld- Inspecta Co.

INSPECTATTT DiagramTT Diagram

Time

Tempe

ratu

re

Steel Make Up

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