Effects of Shielding Gas on the Depth, Width and Hardness of 17-4PH Stainless Steel during TIG Welding

The present study investigates the effects of type of shielding gas on the depth, width and hardness of 17-4PH stainless steel. For this purpose, pure He, pure Ar and 80%Ar + 20% He were used as shielding gases in TIG welding of 17-4PH SS. Weld depth and width of specimens were measured by macro etching. Microstructure of welds was studied by using SEM technique. Moreover, micro Vickers hardness test was accomplished to gauge the hardness of welds. Results showed that specimen welded with pure He has the highest hardness values in the weld zone due to the reduction of δ-ferrite formation in the martensitic matrix. Furthermore, owing to the lower thermal conductivity and heat input of Ar gas, specimen welded by pure Ar has the shallowest and narrowest weld bead. However, due to produce hotter arc by addition of He in shielding gas, enhancements observed in the weld depth and width of specimens welded with pure He and 80%Ar + 20% He.