TO STUDY THE MECHANICAL PROPERTIES OF WELDED JOINT OF MILD

STEEL & EN-31 WITH CHANGE PARAMETER OF MIG WELDING.

AUTHOR :- PAWAN KUMAR (M.TECH)

ABSTRACT

This study was carried out to investigate To study the mechanical properties of welded joint of mild steel & EN-31 with change parameter of MIG welding. The study reveals the influence of current and voltage on the weld bed of steel as well as the mechanical properties of the metal. The samples were welded together by metal inert gas welding process and wire feeder speed selected against the values of current and voltage after which various tests were performed on the welded samples. In large steel fabrication industries such as ship making, and train guide way, the problem of residual stresses and overall distortion has been and continues to be a major issue. In the last few decades, various research efforts have been directed at the control of the welding process parameters aiming at reducing the distortions and residual stress effects. Yet in actual practice, large amounts of resources are still being spent in reworking welds, which in turn increases the production cost and delays work completion.

It is assumed that in order to reduce the residual stresses and distortions from a welding

operation, it is necessary to understand the effects of welding process parameters on various

mechanical properties of material. In this dissertation, the effect of various process parameters on

hardness, impact strength, chemical composition and microstructure of material. Also, a study

has been conducted to assess the effects of welding current, welding voltage, wire feeder rate on

gas welding responses as applied to mild steel and EN-31 welding. A single pass butt joint gas

welding has been chosen in this study. The result shows that all parameters have a significant

effect on the various properties of material. Hence, after studying the effect of various

parameters on weld quality, it might be possible to select the best combination of various

parameters to get a good quality weld. It will help in reducing the residual stresses and distortion

in the welding.

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Introduction

1.1 Welding :-

Welding is a process of joining two similar or dissimilar metal by metal fusion, with or without

the help of pressure and with or without the use of filler metal. The fusion of metal takes place

by heat. That heat may be produced by chemically reaction, friction between two joining metal

& resistance. In the end of the 19th century, the process of joining was forge welding in which

black smith had used for to join metal by heating and hammering process. Arc welding were

among the 1st processes to develop late in 19th century and resistance welding after this. In 20th

century during world war I and world war II increase the demand for reliable and expensive

process of joining technique. During world war many welding process were developed it also

including manual techniques for example-shielded metal arc welding .many energy sources are

used for welding process like :- flame ,beam(electron),laser beam and friction of two joining

metals during process etc. Welding arc are performed in different -different environment. It may

be used in open place and can be under water. Many precautions are necessary for welding

process. These precautions to avoid burs, electricity shock, vision damage and from harmful

flames and gases .Now days semi-automatic , full automatic welding are very most popular in

industries work like - MIG welding, slag welding, flux welding and submerged welding etc.

Development continued with introduced of beam (laser ,Electric), welding, friction welding in

the late half of 20th century. Now days robot welding are most popular welding for industries

work. In this field researcher continue working for develop advice welding techniques and gain

greater understanding of welded quality. There are many types of welding process are used for

industries work. These welding process are very usefully for joining ferrous and non-ferrous

metals .Due to welding process industries work became easy. Various welding process are used

for industries purpose.

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In general, various welding and allied processes are classified follows :-

• Gas welding

• Arc welding

• Resistance welding

• Solid state welding

• Thermo- chemical welding process

• Radiant energy welding process

Application of welding :-

There are many type of application of welding like as:-

• Automobile construction

• Railroad equipment

• Ships

• Aircraft construction

• Building construction

• Pressure vessel

• Storage tanks

• Piping and pipe lines

• Household furniture

• Fabrication of jigs and fixture

• Bridge construction

• Fabrication of machine tools

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Metal Inert Gas welding (MIG):-

It developed in BM institute in year 1948,developed by H.E Kennedy .During development H.E

Kennedy used a small diameter electrode and a power source with constant voltage .But it had

high deposition rate .It had some limit like very use fully for non-ferrous material with high

cost. There also had some disadvantages like it was very costly with inert gases .In year 1953 it

was used with carbon dioxide gas. So Due to this gas it became popular in welding process and

gained same advantages such like economical for sheet metal work and also could be used easily

in thin material work with smaller electrode wires and more advanced power sources. It was

historical development in welding process. In the early year 1960 a small amount of oxygen with

carbon oxide was added in welding process it became popular in industries field. Now days its

known as pulsed spray arc variation welding. In 1950 and 1960 gave the process more

versatility. t is very most popular in welding process. Now days MIG welding performed by

robot in industries field. The metal inert gas welding is increase employed for fabrication in

many industries .This can used for all position welding. The basic necessary equipment is a

welding gun, a wire feed, power source, wire, and shielding gases.MIG welding can be

intergraded into the robotized, production canters .these advantages have motivated many

researcher to study MIG welding process in detail. Gas metal arc welding is an arc welding

process that used an arc between a continuously feed metal electrode and work piece .It is also

known MAG (metal active gas) welding involves the gases like carbon dioxide and oxygen. A

variant of the GMAW process uses a tubular electrode filled with metallic powders to make up

the bulk of the core material .Such electrode may or may not require a shield gas to protect the

molten weld pool from oxidation.MIG welding used for Al ,MS, EN-31,SS,copper and nickel

metal alloys .In which heat generate between electrode and work piece.MIG welding may be

automatic or full automatic welding.MIG welding also used with a constant direct voltage power

source. We can used it with constant current as well as AC source. Globular, short circuit, spray

and pulsed spray, are metal transfer method in MIG welding process. These all transfer methods

have advantages as well as limitations. There are following shield gases used for avoid oxidation

on weld pool like Argon ,carbon dioxide and helium gas these are mostly useable gases during

welding process.

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Welding polarity :- MIG welding done with reverse polarity that means electrode connected

with positive side of battery and negative with work piece .But in flux core (gas less) welding

done with straight polarity mean electrode connected with negative side of battery and work

piece connected with positive side of battery. According experiment electrons flow from

negative to positive side of battery and causes heat build up at the positive side. Electrode used

mean wire is ER70S6 wire thickness is like between 0.023 to 0.045 used for heavy industrial

purpose. Wire ER7OS6 used for steel work .Code ER7OS6 mean

ER-A filler rod used with wire feed or TIG welding

70-70,000 tensile strength /inch 2

S- solid wire.

6- Availability amount of cleaning and oxidation agents in feeding wire.

Chemical composition of the wire is given in Table 1. The pure Argon as shielding gas is used.

C M n Si p s Cu

0.060-0.16 % 1.40-1.8 % 0.8-1.14 % <0.025 % <0.025 % <0.05%

Table 1.1 Chemical Composition of Wire

1.8 Mild steel:-

Mild steel, also known as plain-carbon steel, is the most common form of steel because its price

is relatively low while it provides material properties that are acceptable for many applications,

more so than Fe Mild steel is the least expensive of all steel and the most common steel used.

Used in nearly every type of product created from steel, it is weld able, very hard and although it

easily rusts, very durable. Containing a maximum of 0.29% carbon this type of steel is able to be

magnetized and used in almost any project that requires a vast amount of metal. Its structural

strength prevents it from being used to create load-bearing girders and structural beams.

Many of the everyday objects that are created of steel are made using mild steel, including

automobile chassis, motorcycle frames, and most cookware. Due to its poor corrosion resistance,

it must be painted or otherwise protected and sealed in order to prevent rust from damaging it. A

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light coat of oil or grease is able to seal this steel and aid in rust control. Unlike high carbon,

mild steel is easily welded. The properties of the steel allow the electrical current to travel

through the metal without distorting the makeup of the material. Some types of high-carbon

steel, such as SS require special techniques in order to properly weld the material. Being less

brittle than high-carbon steels, the mild variant is able to flex and give in construction projects

where a higher-carbon version could simply break.

Most of the pipeline in the world is created using mild steel. This allows the pipe to not only be

easily welded into place, but also lets the pipeline flex and avoid cracking and breaking under

pressure. The corrosive properties of the steel pipeline mean that it must be properly sealed

through painting or a process often used on pipelines that involves wrapping the pipe with a

corrosive-resistant material. Mild steel is a type of steel alloy that contains a high amount of

carbon as a major constituent .An alloy is a mixture of metals and non-metals, designed to have

specific properties. Mild steel is the type of steel, which is used in 84% of all steel applications in

the United States of America. This article will talk about mild steel properties and enlighten you

about why exactly is it called 'mild' and what it really means.

Mild steel absorb shocks it is having bright fibrous structure. It can be easily forged and welded

and it is malleable and ductile. Its tensile strength is better than cast iron and wrought iron but

compressive strength is better than wrought iron but less than cast iron and melting point of mild

steel is 1400 C.

1 .EN-31

EN-31 is very important metal from EN series. It is very most popular in manufacturing

industries. It have good surface finishing and harness. EN having following series like EN-8,EN-

24 and EN-31 but it is very usefully in manufacturing .EN-31 have good machining properties .

It is used for ball bearing .shear blades , modeling die ,industrial gauges ,axles , spindle and for

high hardness components . EN-31 is a alloys steel that which is very popular in manufacturing

field. Alloys steel is defined as a steel alloyed have variety of elements in total amounts range

from 1 to 50 %. Alloys steel classified into two class that is low alloy and high alloy .Low alloys

steel have lower than 4-5% alloy and other hand high alloys steel have more than 8%alloys. EN-

31 have following elements like most common -Mn, Ni, Cr, V, Si, and boron & less used

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alloying elements are Al , Co, Cu , Nb , Ti and W.EN-31 have high carbon alloy steel which

that offer a high hardness with abrasion resistance and compressive strength . It is very popular

in manufacturing of industrial gauges and dies. EN-31 is a good quality steel and most useable

metal in world. It also have good wear resistance properties .Forging at 1000c° – 1050c° but heat

slowly and also cool slowly at forging process.EN-31 is supply in the annealed and machining

condition . It anneal solely at 800c~810c and also cool slowly. EN-31 heat at 700c° and carefully

cool.

Chemical elements :-

Fe- 98.721 , C-0.911Si-0.272, Mn-0.570,P-0.0344,S-0.0410,Cr-1.231,Mo-0.0035,Ni-0.0711,

V-0.0153, Cu-0.0618AL-0.0260, Nb-0.0051, Ti-0.0060, B-0.0001 Co-0.0108, W-0.0104, Sn-0.0022

Mechanical Properties of Steel :-

• Hardness

• Toughness

• Brittleness

• Malleability

• Ductility

• Tensile strength

The above listed properties help in determining how an alloy or a metal would behave under

load. Now explain one by one.

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Literature Survey

The principles of gas metal arc welding began to be understood in the early 19th century,

after Humphry Davy discovered the short pulsed electric arcs in 1800.VasilyPetrovindependently

produced the continuous electric arc in 1802. It was not until the 1880s that the technology

became developed with the aim of industrial usage. At first, carbon electrodes were used

in carbon arc welding. By 1890, metal electrodes had been invented by Nikolay HYPERLINK

"http://en.wikipedia.org/wiki/Nikolay_Slavyanov"Slavyanov and C. L. Coffin. In 1920, an early

predecessor of GMAW was invented by P. O. Nobel of General Electric. It used a bare electrode

wire and direct current, and used arc voltage to regulate the feed rate. In 1926 another forerunner

of GMAW was released, but it was not suitable for practical use. Many of investigators have

suggested various methods to explain the process parameters effecting on mechanical properties

of weld metal of steel.

M.St. Weglowski a, Y. Huang b, Y.M. Zhang b:-

The Measurements of metal transfer are presented in the GMAW process in the range of welding

wire speed from 150 inch/min to 240 inch/min[4]. The measurement system is based on a high

speed camera and it can measure the metal transfer at 3000 frames per second.Effect of welding

current on the metal transfer are evaluated using dimensional and kinetic analysis.

E. Mahdi, E. O. Eltai, A. Rauf:-The behavior of MIG welded and un-welded AA 6061 T6 were investigated using a series of

electrochemical measurements and mechanical tests. The Heat affected zone was more

susceptible to corrosion showing severe pitting corrosion comparing to the basemetal[5]. The

hardness of the welded specimens was increased as we moved away from the weld centre and

Torsion welded specimens were broken at the heat affected zone suggesting softness of this area

due to the impact of MIG welding.

G. Haragopal, P V R Ravindra Reddy and J V Subrahmanyam:-

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They presented a method to design process parameters that optimize the mechanical properties of

weld specimen for Al alloy, used for construction of aerospace wings. The process parameters

considered for the study were gas pressure, current, groove angle and pre-heat temperature.

Process parameters were assigned for each experiment. The experiments were conducted using

the L9 orthogonal array. Optimal process parameter combination was obtained. Along with this,

identification of the parameters which were influencing the most was also done[6]. This was

accomplished using the S/N analysis, mean response analysis . Mechanical properties obtained

for three samples of each run were obtained. Signal to noise ratio for each quality (S/N) ratio for

each quality characteristic was calculated, significant parameters were identified and optimum

input parameter for each quality characteristic were predicted from S/N values and mean

response. Analysis of variance ascertained significant parameters identified through S/N

analysis. A confirmation test was conducted at optimum conditions to ensure correctness of

analysis.

Suresh Kumar:-It discuss about micro structural development during MIG welding of copper with iron filler.

During the experimental work they consider voltage, current and travel speed as welding

parameter. They investigate needle shaped morphology of iron matrix typical of marten site and

at copper iron interface bended microstructure was observed which varied with travel speed.

Abbasi..K, Alam S Khan .M.J :-

MIG is carried on 144mm long x 31mm wide & 10mm thick bright drawn, mild steel .Increase in

pressure of shielding gas is studied through variation of welding parameters like feed rate and arc

voltage on penetration. The vessel was pressurized with argon-carbon dioxide mixture to

absolute pressure of 7,14, 29, 58, 115, & 230bars[7].The metal transfer modes were controlled

by changing the wire feed rates in the range of 3.81m/Min to 6.1mm/min. The result was found

that along with increase in pressure the arc voltage must be increased in order to get good weld

bead. Higher the pressure, density of fumes gets increases. MIG welding can be carried up to

pressure of gas 230bar.

M.AgkaKhani et al:-

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This research show studies for the material IS 2062 ES250 Mild steel and take input parameter as

wire feed rate(W),welding voltage(V),nozzle to plate distance(N),welding speed (s) and gas flow

rate (g) and the response was the relationships between the weld dilution and the five

controllable input welding parameters such as wire feed wire, welding voltage, nozzle-to-plate

distance, welding speed, gas flow rate[8]. And it was found that among main input welding

parameters the effect of wire feed rate is significant. Increasing the wire feed rate and arc voltage

increases the weld dilution where as increasing the nozzle to plate distance the welding speed

results in decreases weld dilution and gas flow rate did not affect the weld dilution.

M.Suban,J.Tusek:This research establish the influence of the shielding medium used on quantity of the filler

material melted. A comparison was made between the melting rate in welding with a solid wire

and a cored wire, respectively[9]. The melting rate in welding with the cored wire is higher than

in welding with the solid wire the condition being same. It is quite interesting that at high current

melting rates are higher in CO2.

Pawankumar, Dr.B.K.Roy:-In this study it was worked carried out on plate welds AISI 304 & Low Carbon Steel plates using

gas metal arc welding (GMAW) process. Taguchi method is used to formulate the experimental

design. Design of experiments using orthogonal array is employed to develop the welds .The

input process variables considered here include welding current,welding voltage & gas flow rate.

A total no of 9 experimental runs were conducted using an L9 orthogonal array the ideal

combination of controllable factor level was determined for the hardness to calculate the

signal-to noise ratio After collecting the data signal-to-noise ratios were calculated as used in

order to obtain optimum levels for every input parameter. The Nominal-the-better quality

characteristic is considered in the hardness prediction

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Problem Formulation

MIG is currently one of the most popular welding methods, especially in industrial

environments. It is used extensively by the sheet metal industry and by extension, the automobile

industry. There are the many type of problem found when change in mechanical properties

during welding like dimensional inaccuracies and misalignments of structural members, which

can result in corrective tasks or rework on the work piece. Due to this increases the cost of

production, waste material and leads to delays. In industries, for example, expenses for rework

such as straightening could cost money as well as time .The problem of change in properties, are

always of great concern in welding industry. In order to deal with this problem, it is necessary to

predict the amount of change in properties like hardness, impact strength, toughness,

microstructure etc. during welding operations. Once the techniques to predict the change the

properties are identified, then the problems can be controlled accordingly.

Within the welding procedures, there are many factors such as welding process type, welding

process parameters, welding sequence, preheat patterns, level of constraint and joint details that

contribute to the distortion of the welded structure. Knowing which parameters have an effect on

the quality of the weld and which parameters give the most significant effect on the weld quality

are the main issues in welding industry. There certain factors on which the selection of welding

process depends like volume of the material to be welded, types of joint obtained, base metal. In

every welding process there are certain parameters on which weld quality depends. In arc

welding also there are certain parameters on which weld quality depends. There are various

welding parameters on which various properties of weld depend. The objective of this research

is first, to weld the piece on the different parameters. Then, after to check the hardness, impact

strength, chemical composition and microstructure of steel on different parameters. The ultimate

objective of this research is to get a suitable set of welding parameters on which the properties of

the weld material and base should be almost same. There is not much difference in there

mechanical property. This will ultimately help in reducing residual stresses and distortion in

welding. So the main objective of this research is to provide a suitable set on parameters to get a

best possible weld.

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Experimental Analysis

In this chapter we are going to study the various machines and equipments like Welding

Machine, Hardness Tester, Impact Testing Machine and other equipments used during

experimentation.

Welding Machine:-We used MIG welding for joining MS and EN-31 metal with co2 gas cylinder .Model ESAB

MIGMATIC 400Amp.This is very popular in manufacturing field.

Welded Specimen:-

In this study Mild Steel SAE 350 and Stainless Steel SAE 304L Grade is used. First Step in this

study we cut the Mild Steel and Stainless Steel in to small pieces for welding the specimen. After

that we done MIG welding on these piece shown in the figure. In the figure shows that the butt

joint welding are used for this study. Before Welding LBH of pieces is (79*49*5) mm And After

.2 mm increment in length.

After the MIG welding operation we plan the weld bead on grinding machine in workshop for

various testing. These shows in below figure.(AG4 Grinder)

After preparing the various specimen, next step is to do various testing. For this various

specimen are cut from these welded pieces and perform various testing .

Testing:-

4.3.1 Hardness MeasurementTest:-There are three types of tests used with accuracy by the metals industry; they are the Brinell

hardness test, the Rockwell hardness test, and the Vickers hardness test. Since the definitions of

metallurgic ultimate strength and hardness are rather similar, it can generally be assumed that a

strong metal is also a hard metal. The way the three of these hardness tests measure a metal's

hardness is to determine the metal's resistance to the penetration of a non-deformable ball or

cone. The tests determine the depth which such a ball or cone will sink into the metal, under a

given load, within a specific period of time. There are the many type of Hardness test is used in

today’s technology but in this study Rockwell Hardness test is used.

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Rockwell Hardness Test:-Rockwell tester use small penetrators and smaller loads than does the Brinell tester. In this two

types of indenters. The Rockwell Hardness test is a hardness measurement based on the net

increase in depth of impression as a load is applied. Hardness numbers have no units. The higher

the number in each of the scales means the harder the material [20]. Hardness has been variously

defined as resistance to local penetration, scratching, machining, wear or abrasion, and yielding.

The multiplicity of definitions, and corresponding multiplicity of hardness measuring

instruments, together with the lack of a fundamental definition, indicates that hardness may not

be a fundamental property of a material, but rather a composite one including yield strength,

work hardening, true tensile strength, modulus of elasticity, and others. In the Rockwell method

of hardness testing, the depth of penetration of an indenter under certain arbitrary test conditions

is determined. The indenter may either be a steel ball of some specified diameter or a spherical

diamond-tipped cone of 120° angle and 0.2 mm tip radius, called Brale. The type of indenter and

the test load determine the hardness scale.

A load of 100 kg is first applied, which causes an initial penetration and holds the indenter in

place. Then, the dial is set to zero and the major load is applied. Upon removal of the major load,

the depth reading is taken while the minor load is still on. The hardness number may then be read

directly from the scale. The hardness of ceramic substrates can be determined by the Rockwell

hardness test, according to the specifications of ASTM E-18. This test measures the difference in

depth caused by two different forces, using a dial gauge. Using standard hardness conversion

tables, the Rockwell hardness value is determined for the load applied, the diameter of the

indentor, and the indentation depth. The hardness testing of plastics is most commonly measured

by the Rockwell hardness test or Shore hardness test. Both methods measure the resistance of the

plastic toward indentation. Both scales provide an empirical hardness value that doesn't correlate

to other.

3 Impact Test:-The property that is measured in impact test is the energy absorbed in fracturing the specimen of

standard dimensions and standard notch. This property measured in N-m or J IS also often

referred to as impact toughness or strength.

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The impact testing machine as shown in fig. is a rigid strong structure of two columns on a heavy

base. The columns carry a heavy swinging pendulum at their top which swings on frictionless

pins and a support platform at the buttons for the specimen. When the pendulum is in its vertical

position its striking edge is in level with the central cross section of the specimen. A circular disc

scale is mounted centric with the pin of the pendulum which reads its position.

Microstructure Testing:-Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed

by a microscope. The microstructure of a material can strongly influence physical properties

such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature

behavior, wear resistance, and so on, which in turn govern the application of these materials in

industrial practice[21]. A microstructure is the way a material comes together on a very small

scale. An object's microstructure is not visible by the naked eye, although the patterns present at

the microscopic level may replicate at a larger level. This larger level is the macroscopic level; it

will give an observer a basic impression of the material’s underlying design. The object’s

microstructure determines the majority of its physical properties. There are four main categories

that materials fall into based on their microstructure: ceramic, metallic, polymeric and

composite.

A material’s physical structure will appear to change depending on how closely you look at it.

When an object is held at arm’s length, it looks different than if it is a hand’s width away from a

person’s face. The same is true when an object is observed under a microscope. In order to create

a standard definition of microstructure, the power of the magnification used to look at it is no

more than 25x. When the structure is observed at a higher or lower power, it looks different.

These other observable structures, particularly the smaller ones, can have a significant impact on

the properties of the object. Instead of expanding the definition of microstructure, the elements

that make up the microstructure are changed to accommodate differences in underlying structure.

4.3.5 Microstructure testing process :-

After the MIG welding operation welded pieces are cut out on the power hacksaw. The portion

cut out from the welded specimen is such that it contains weld bead with uniformity and with

high penetration. After cutting by the power hacksaw as shown above the specimen is cut in such

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a way that the weld bead remains in the centre and a good grip can be provided by the hand for

the further operations. Then a filing operation is provided to all the faces of the weld bead

sample. After filing by the help of hammery paper hamming process is carried out. In this we

use hammer paper of grade 1, grade2, grade3 and grade 4. By hamming process a very neat and

clean surface is obtained on which microstructure is to be seen. After using the hammery paper

buffing process is carried out by the help of buffing cloth on the buffing machine.

Result & DiscussionOn the basis of above experiments and research we can determine the effect of the various

process parameters on the mechanical properties of mild steel and stainless steel . During this

process we select various parameters and consider their effect on hardness, impact strength,

microstructure and chemical composition.

The various process parameters which we select in this study :-

1. Voltage

2. Current.

3. Wire feeder speed

In this dissertation I consider the effect of the above mentioned parameters on the following

properties of the mild steel and EN-31.

1. Hardness

2 .Impact strength

3. Microstructure

4. Chemical composition

The observation shows the effect of above mentioned parameters on hardness, impact strength,

microstructure and chemical composition.

Effect of various parameter on Hardness :- During the MIG welding operation wire feeder speed is selected against the voltage and current

and various readings are taken. The following table and graph shows the variation of harness

with current and voltage.

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Sr. No voltage Current Weld zone Hardness

HAZHardness

1 22 80 48 32

2 24 90 50 40

3 26 98 45 38

4 28 110 25 20

5 30 122 40 20

6 32 135 35 20

2Effect of wire feeder speed :-We took the reading by adjusting wire feeder speed during MIG welding process shown in table

below.

Sr.no Wire feeder speed

Weld zone Hardness

HAZ Hardness

Out come

1 4 48 32 Waviness of Bead

2 7 50 40 Good weld

3 10 45 38 Spatter on piece

4 13 25 20 Excessive deposit of

metal5 15 40 20 Crack on

weld zone6 19 35 20 Incomplete

fusion

Effect of Wire Feeder Speed on Impact Strength :-For examine the effect of wire feeder speed on impact strength .we took the values of wire feeder

speed and study their effect on impact strength. The following table and graph shows the

variation of impact strength with wire feeder speed.

Sr.no Wire feeder Impact strength (joule)

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speed1 4 95

2 7 110

3 10 85

4 13 76

5 15 70

6 19 65

Table 5.3 For Varying Wire Feeder Speed and Impact Strength

4 Microstructure Testing Results :-The microstructure tests are carried out on the microscopes equipped with inbuilt cameras.

During this research the microstructure of base metal, welded joint and Heat effected joint is

investigated..

The microstructure of Weld joint is shown in figure 5.10. The microstructure shown in figure

consist of martensite. Martensite named after the German metallurgist Adolf Martens. Most

commonly refers to a very hard form of steel crystalline structure but it can also refer to any

crystal structure that is formed by defussion less transformation. It includes a class of hard

minerals occurring as lath- or plate-shaped crystal grains. Martensite is present at grain

boundaries results in increase in hardness.

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Chemical composition testing results :- Weld Zone consist various types of elements like as :- Iron, Carbon, Silicon , Manganese,

Sulphar, Phosphorus, Nickel, Chromium ,Molybdenum, Copper, Cobalt Vanadiu .

Chemical composition of mild steel & EN-31:-

Average

Fe- 98.613, Fe- 98.721,

C-0.311, C-0.911,

Si-0.162, Si-0.272,

Mn-0.4977, Mn-0.570,

P-0.0365, P-0.0344,

S-0.0278, S-0.0410,

Cr-0.1087, Cr-1.231,

Mo-0.0010, Mo-0.0035,

Ni-0.0450, Ni-0.0711,

Cu-0.127, Cu-0.0618,

V-0.0059, V-0.0153,

AL-0.0116, AL-0.0260,

Nb-0.0078, Nb-0.0051,

Ti-0.0050, Ti-0.0060,

B-0.000 B-0.0001,

Co-0.0140, Co-0.0108,

W-0.0054, W-0.0104,

Sn-0.0131 . Sn-0.0022,

Pb-0.0075,

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CONCLUSION & FUTURE SCOPE

6.1 CONCLUSION :-

This research helps in determining the correct welding parameters in Gas Metal Arc Welding

process. During this research the change in hardness, impact strength ,microstructure and

chemical composition at various process parameters is investigated. The original properties and

the values of these the properties are different. This means that during welding there is always

some changes in the properties of material. . These parameters really affect the welding quality

which can be seen from above discussion. The following conclusions are derived from above

research.

• There is increase in hardness and small increment in impact strength when current

increases when we start our wire feeder speed from 2.2 to 7 according literature review.

In which observed that after wire feeder speed increase with current and voltage hardness

and impact strength 1st goes down then small increase .

• The microstructure also changes with increase in current. Originally mild steel contains

ferrite and pearlite at grain boundaries. As current increases ferrite is converted in

cementite and martensite. Due to this increment in hardness.

• There is small increase in hardness and impact strength with increase in current .

• There is small increase in hardness and impact strength with increase in voltage

SCOPE FOR FUTURE :-

• There is also a lot of future scope for Gas metal arc welding researches. During this

research only three parameters are investigated only for four properties. Similarly other

parameters can be used to find out the other mechanical properties .The effect of the

process parameters can be investigated in other welding processes also.

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References

• R.W. Messler, Principles of Welding, Processes, Physics, Chemistry, and Meallurgy,

Chapter 3, John Wiley & Sons, New York, 1999.

• http://www.wisegeek.org/what-is-mild-steel.htm

• .http://en.wikipedia.org/wiki/Carbon_steel.

• M.St. Wêglowski. Y. Huang , Y.M. Zhang (2008) “ Effect of welding current on metal

transfer in GMAW” International Scientific Journal, Vol-33 pp 49-56.

• E. Mahdi, E. O. Eltai, A. Rauf, (2014)”The Impact of Metal Inert Gas Welding on the

Corrosion and Mechanical behavior of AA 6061 T6”Int. J. Electrochem. Sci, Vol-9 pp

1087-1101.

• G. Haragopal, , P V R Ravindra Reddy, G Chandra Mohan Reddy and J V

Subrahmanyam, (2011)“Parametric design for MIG welding of Al-65032 alloy using

Taguchi Technique”, Journal of Scientific and Industrial Research, Vol. 70,, pp.844-8.

• Abbasi..K, Alam S Khan .M.J(2011),” An experimental study on the effect of increased

pressure on MIG welding arc”, International journal of applied engineering research,

Dindigul ,Vol2,No1.

• M. Aghakhani , E. Mehrdad, and E. Hayati (2011), "Parametric Optimization of Gas

Metal Arc Welding Process by Taguchi Method on Weld Dilution" International Journal

of Modeling and Optimization ,pp216-220

• M.Suban,J.Tusek (2001) “ Depedence of melting rate mig/mag welding type of shielding

gas used journal of material processing technology pp 185-192.

• Pawan Kumar (2013), “Parametric Optimization of Gas Metal Arc Welding of Austenitic

Stainless Steel (AISI 304) & Low Carbon Steel using Taguchi’s technique”, International

Journal of Engineering Research and Management research, Vol. 3, Issue 4, pp.18-22.

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