analysis of heat affected zone of mild steel · pdf filespecimen developed due to mig welding...

399

Int. J. Mech. Eng. & Rob. Res. 2014 Praveen Kumar Yadav et al., 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 3, July, 2014

© 2014 IJMERR. All Rights Reserved

Research Paper

ANALYSIS OF HEAT AFFECTED ZONE OF MILD STEEL

SPECIMEN DEVELOPED DUE TO MIG WELDING

Praveen Kumar Yadav1*, Md Abbas1 and Shishir Patel1

*Corresponding Author: Praveen Kumar Yadav � [email protected]

The Gas Metal Arc Welding is the most widely used for long continuous welds also it is versatilein nature as spot welds can also be per formed by GMAW. Process requires relatively simpleand lesser skilled labors, so it is mostly automated and once welding parameters established itshould be possible to produce repeatable welds. It is also called as MIG welding. As there is agreat influence of welding conditions on behavior of heat affected zone (HAZ) so the presentwork investigates the effect of welding condition according to mechanical properties of mildsteel and presents the optimum welding condition through the evaluation about the weld abilityof mild steel by the welding conditions such as the welding passes, voltage variation, current,variation, and change in thickness of mild steel flats. In order to find out optimum weldingcondition by the mechanical properties mild steel (0.134% carbon) was selected as a specimenhaving thickness 5, 8,16mm were prepared for experiment. Specimens were welded in therange of 20-24 Volt, 130-150Amp and test pieces out of theses for test of tension, impact andhardness and micro structure have been extracted. The experimental result revealed that withincrease in voltage there is increase in penetration so using the parameters further welding wasperformed. Results show that with increase in current there is increase in hardness of HAZ andultimate tensile strength.

Keywords: Heat affected zone, Mild steel specimen, MIG welding

INTRODUCTION

Selection of the Work Material and

Electrode

Metal inert gas welding is the most versatilewelding and commonly used for making longand continuous weld as it can be easily automated. Metal arc welding was used forexperimentation. The chemical composition

1 Department of Mechanical Engineering, IEC College of Engineering and Technology, Greater Noida.

of the material used is shown in the TableNo. 1.

For welding mild steel work-piecesCopper-coated mild steel (MIG) electrodehaving specifications IS 6419, (AWS A/SFA5.18) manufactured by Ador welding limitedwas selected which has diameter 1.2 mm. Itprovides stable arc and minimum spatter

400


Table 1: Chemical Composition of Materials (wt %)

Material

Mild Steel

under optimum welding conditions. Normallyrecommended with CO2 shielding and canbe used with Ar- CO2 mixtures also. It is allposition electrode meant for MIG welding.Composition of wire is C-0.07-0.14, S-0.025max, Mn-1.40-1.60, O-0.025max, Si-0.80-1.0, Cu-0.5max (% age by weight),mechanical properties of all welded with100% CO2 are UTS-500-550 MP and YS-420-480MP a also it leaves metal free of slagand oxide inclusions and produces soundwelds.

Micro Structural Examination

Micro structural Examination was carried outon Leitz metallurgical microscope. Thephotograph of different zones of weldedspecimen was taken for study. A microstructural photograph of heat affected zonewas taken at 100 magnifications.

The different zones of welded specimenof mild steel can be seen in Figure 4.12 below.

Fe%

99.2

C%

0.134

Si%

0.074

Mn%

0.404

P%

0.056

S%

0.022

Cr%

0.16

Al%

0.002

Cu%

0.009

Figure 1: Different Zones of WeldedSpecimen of Mild Steel

Parent Metal Heat Affected Zone Weld metal Zone

Linear intercept method can be used forgrain size determination from micro structuralphotographs. Length parameter is the meanintercept length.

MPL

×= TL

Where

L = Grain size in mm LT = Total test linelength in mm M = Magnification factor

P = The number of grain boundariesintersecting test line

Mechanical Testing of the Test

Specimens

Hardness Testing:-The Vickers and knooptests make relatively small indentations andare thus well suited for hardness measure-ment of the various regions of the HAZ forfine scale traverses. In Vickers hardness testa know load (P) from 1 to 120 kg dependingon the material to be tested is applied forspecified time to the surface of the materialthrough a square base diamond indenter orpyramid having 136° between opposite faces.The two diagonal of the resulting squareindentation on the test piece are measuredwith a micrometer microscope and averagedD mm is use for calculation of hardness. TheVickers hardness number is calculated as byfollowing equation.

2

1.854PVHN

D=

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RESULTS

This deals with the results of the experimentalfindings of welded joints prepared at differentvoltages, current, number of pass and effectof variation of specimen.

Effect of Voltage on Penetration

Specimens were welded at varying Voltageof 20V, 22V and 24V keeping other conditionsare constant like current=130, wire speed,shielding gas pressure and welding speedetc. By visual observations it was found thatwith increase in voltage there was alsoincrease in penetration as shown below infigures 5.1, 5.2 and 5.3.

Figure 2: Specimen Welded at 20Volts



Specimen welded at 24volts shows fullpenetration for 1.5 mm face width and it givesbest results in terms of penetration.

So by observing the above results theconditions for welding multiple passes usedare 24V and 130Amp, with electrode wire

speed 22.2mm/sec and welding speed of1to2 mm/sec.The specimens were furthertested for hardness.

Effect of Voltage on Hardness

As we can see from the graph betweendistance from the weld centre and hardnessthere is nearly constant variation of hardnessbut suddenly the parent metal next to weldmetal i.e. HAZ there is increase in hardnessbecause there is a thermal gradient betweenwelding heat and atmospheric temperaturedue to this sudden quenching by air there isformation of martensitic structure in HAZcausing increase in hardness. As we can seethere is increase in HAZ hardness withdecrease in voltage.

Figure 5.4: Effect of VoltageVariation With Hardness

Effect of Variation of Thickness on

Hardness of HAZ

For similar conditions like current of 130Amp,24 voltage, welding speed and wire electrodespeed the following results are obtained.

402


Figure 5: Effect of VoltageVariation with Hardness



Table 2: Variation of Hardness with Voltage

Distancefrom

weldbead

center (mm)

0

1

2

3

4

5

6

7

8

9

10

11

12

Hardness(HV)

Voltage=20

190

189

186

190

192.4

184

146

140

135

134.1

133.5

134.2

134.5

Hardness(HV)

Voltage=22

188.1

186

185

187

189.2

184.2

145.2

135

134.2

135.1

135.3

134

135.1

Hardness(HV)

Voltage=24

187.2

185.1

182

184

185.3

165.1

143.8

136.9

133.4

135

135.1

135.2

135

Table 3: Effect of Variation ofThickness on Hardness of HAZ

SpecimenThickness

(mm)

5

8

16

Maximum HAZHardness

(HV)

185.3

200.1

190.5

Maximum UTS(Kg/mm2)

34.8

47.15

44.2

Figure 8: Effect of Variation ofThickness on Hardness of HAZ

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CONCLUSION

By visual inspection it was observed that forincrease in voltage there is increase inpenetration and there is slight increase inHAZ hardness with respect to increase InCurrent. So it may be concluded that usinghigher voltage of 24V better penetration canbe obtained. Also the increase penetrationhas forced to perform rest of multiple passwelding with 24 V and 130Amp current. So24V and 130Amp current is recommendedfor welding the specimens.

REFERENCES

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analysis of heat affected zone of mild steel · pdf filespecimen developed due to mig welding...

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