EFFECT OF ALTERNATE SUPPLY OF

SHIELDING GAS ON MECHANICAL AND

METALLURGICAL CHARCTERISTICS OF

CARBON STEEL GAS METAL ARC WELDING

Presented by

Sreejith T.S.

212110019

Welding Engineering

MME Department

Guided by

Dr. V. Sivan

Professor

Dr. S. Natarajan

Professor

MME Department

NIT TRICHY

Dr. A. Raja

AGM

WRI, BHEL TRICHY

OVERVIEW

• Work plan

• Introduction

• 0bjective

• Mechanical properties of weld metal

1. Tensile test

2. impact test

• Result and discussion

• Reference

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Introduction• Generally discrete alternate supply of shielding gas is a

new technology which alternately supplies the different

kinds of shielding gases in weld zone

• This technology is capable of achieving better quality and

high efficiency using the physical properties of welding

arc

• In GMAW, mixtures of two or more gases are often used

to shield the arc and the molten weld pool in order to

improve the fusion process and weld quality. These mixed

gases can be premixed at a filling plant and delivered in a

cylinder for use at a job site or two gases can be mixed at

the job site using a gas blender or mixer.

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• Shielding gas is very important in GMAW and therefore any

change in gas mix or flow parameters greatly affects the arc

transfer characteristics and resultant weld quality. The

shielding gas system thus greatly impacts productivity and

cost-effectiveness.

• The problem with the current shielding gas systems is mixed

cylinders are expensive and gas mixers are often inaccurate,

therefore more efficient, alternative shielding gas technologies

are of interest

schematic diagram of gas alternator

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• In the case of alternate supply of Argon and CO2 in constant arc length, the welding current and the arc voltage increases and decreases discretely.

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• Argon is supplied into welding arc, the welding current

decreases, and the arc voltage increases. Conversely CO2 is

supplied into welding arc, the welding current increases, and

the arc voltage decreases

• The periodic change of gas and arc pressure, increase the

fluidity of weld pool and reduce of surface tension of molten

metal to make grain of weld zone refine

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OBJECTIVE • The purpose of this investigation is to study the effects of

alternate supply of shielding gas on mechanical and

metallurgical properties of carbon steel using gas metal arc

welding process.

• The investigation will determine if the pulsing of two pure

shielding gases create potential benefits relative to the use of

conventional gas mixtures.

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Work done so far

• Three arc weld metals were produced at nominal heat

input of 1.5 KJ / mm , using a SA 515 Grade 70 base

plate and 1.2 diameter wire, ER 70S-6

• For each welding, different kind of supply of shielding

gas is used, ie 100% CO2, mixture of Ar and CO2 ( 80%

Ar 20% CO2) and alternative shielding of argon and CO2

• Welding parameter used in the experiment were ; wire

feed rate of 10m/ min, welding voltage of 29 V, welding

speed of 240 mm / min and flow rate of gas 22L / min . In

case of alternative shielding gas, time period for supply

of each gas is 0.2 second.

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Work done so far

• For welding , a 150 mm x 250 mm plate of 20mm in

thickness as base metal and 45 degree in groove angle

and 12 mm in root gap as weld joint design is employed

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Work done so far

• Transverse sections were cut from each weldments and

their surfaces prepared for quantitative metallography

• Four rectangular charpy V notch specimen and one all

weld tensile specimen machined from weld metal.

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MECHANICAL TESTINGS

Equipment used - UTE-60

Description of test item - carbon steel all weld tensile specimen

Size of specimen -180mm*Dia18mm and diameter of reduced section 12.5+/-0.25mm

ASTM A370 standard

1. TENSILE TEST

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UTS(MPa)

YS (MPa)

% elongation

100% CO2 569 482 29

80% Ar&20%CO2 591 493 31

Alternate supply of shielding gas

597 495 31

2. IMPACT TEST

Test Standard: AWS B4

Testing Temperature : 270C

Specimen Size: 10*10*55mm

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toughness value joule at 280 C

100% CO2 132, 136, 134

80% Ar&20%CO2 140,142,148

Alternate supply of shielding gas

156,160,158

Result and discussion

• The weld done with alternate shielding gas has more

toughness as compared to other two cases. This can be

explained on the basis of higher acicular ferrite percentage

in the weld metal.

• The presence of acicular ferrite will increase the

toughness of the material. Weld metal with high

proportion of acicular ferrite posses superior fracture

toughness because the randomly oriented short

interlocking ferrite plates along with it fine grain size

provide maximum resistance to crack propagation.

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Work to be done

• Chemical composition of weld metal APRIL 4-10

• Microscopic Analysis APRIL 10-15

• Quantitative analysis of the weld metal

microstructures APRIL 15-25

• Spectroscopy APRIL 25

• Microscopic study of inclusion and Volume

fraction of inclusion APRIL 25-30

• Thesis preparation MAY 1- 25

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Reference

• I.S. Kim, J.S. Son, H.J. Kim B.A. Chin( 2006) Development of a mathematical model to

study on variation of shielding gas in GTA welding. Journal of achievements in Materials

and manufacturing engineering

• S. Mukhopadhyay, T.K. Pal(2006), Effect of shielding gas mixture on gas metal arc

Welding of HSLA steel using solid and flux-cored wires, International Journal of

Advanced Manufacturing Technology, 29: 262–268

• Kang, B. Y,., Kang, M. J., Kim, H. J., & Kim, I. S. (2009) Characteristics of alternate

supply of shielding gases in aluminum GMA welding. Journal of Materials Processing

Technology, 209, pp. 4716-4721.

• S. Liu and D. L. Olson (1987) The Influence of Inclusion Chemical Composition on Weld

Metal Microstructure Journal . Mater. Eng. (1987) 9:237-251

• M. Ferrante, and R.A. Farrar, (1982) "The role of oxygen rich inclusions in

determining the microstructure of weld metal deposits," Journal of Materials Science, vol.

17,p. 3293.

• S. Liu and D.L. Olson. (1986) The Role of Inclusions in Controlling HSLA Steel Weld

Microstructures," Welding Journal, vol. 65(6); pp. 139-s-150-s.

• Sudarsanam Suresh Babu (2004) The mechanism of acicular ferrite in weld deposits

Current Opinion in Solid State and Materials Science 8 (2004) 267–278

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THANK YOU

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