Welding Investigation and Prediction of Tensile Strength of 304 Stainless Steel Sheet Metal Joint by Response Surface Methodology

This study deals with an investigation of welding behaviour of 304 stainless steel sheet metal in term of joint strength and microstructure. Composition analysis of the stainless steel plate and ER308 filler rod was performed using X-ray fluorescence and SEM-EDX. Tungsten inert gas (TIG) welding was done on SS 304 2B plate with thick-ness of 1.2 mm in Coraza Systems Malaysia Sdn. Bhd using a KADEYOU machine. Response surface methodology (RSM) was employed to develop mathematical relation-ships between the welding process parameters (i.e, welding current, filler size and flow rate of the shielding gas) and the output variable of the weld joint (ultimate tensile strength) to determine the welding input parameters that led to the desired weld quality. Comparison between measured and calculated results was in good agreement indicating that the developed models can predict the responses adequately within the limits of welding pa-rameters being used. High welding current (50A) cause microstructure become finer and increase in tensile strength while low current (30A) caused root of the metal plate not weld completely which weakened the joint (724.84 MPa and 718.33 MPa, correspond-ingly). The smallest filler (1.6 mm) was good for tensile strength (745.96 MPA) com-pared to the largest filler (2.4 mm and 720.90 MPa strength) because high heat energy used to melt the large filler also overheated the metal base that cause crack formation. High flow rate (14 cfh) caused tensile strength to drop (738.49 MPa) due to the turbu-lence in the molten metal compared to the lowest flow rate (10 cfh and tensile 756.75 MPa strength).