Effect of shielding gas combination on microstructure and mechanical properties of stainless steels by MIG welding

One of the most suitable methods for stainless steel welding is gas metal arc welding. The quality of weld joined using gas metal arc welding is directly related to the right welding parameters and choice of the best shielding gas. Additionally, the shield gas is chosen by considering characteristics such as molten weld metal's chemical-metallurgical interaction, heat transfer capacity and cost of gas. In this study, different shielding gas combinations were used for welding of 316 austenitic stainless steel via metal inert gas (MIG) method and their effects on mechanical and microstructural properties were investigated. Pure argon (100% Ar), 98.5% Ar + 1.5% H2 and 95% Ar + 5% H2 were used as the gas combinations. Metallographic examinations were performed to determine joined samples' macro and microstructural properties. Furthermore, tensile, hardness and three point bending tests were conducted to specify mechanical properties. Lastly, 24, 48, 72 hours salt mist corrosion tests were carried out and results are examined using EDS analysis to reveal corrosion behaviours of welded samples. After all tests and metallographic examinations, macro and microstructural differences were observed in heat affected zone (HAZ) and weld metal. After mechanical tests, no significant difference is observed between joints welded using three different gas combinations (100% Ar, 98,5% Ar + 1,5% H2 and 95% Ar + 5% H2). However, a slight decrease of tensile strength was observed with increasing hydrogen content. Fractures were formed on the base metal after each tensile test. No crack or tear failure were detected on the welding zone as a result of three point bending tests. The hardness of the weld metal was measured as lower than HAZ and base metal for all welds prepared using different parameters. An increase of the corrosion damage with longer test duration and the breakage of the passive chromium oxide layer were noticed.