The effect of shielding gas on weldability of the AISI 420 martensitic stainless steel

Most of weld defects occurring in the welding of martensitic stainless steels are caused by the presence of hydrogen. Thus, the effects of hydrogen in the weld zone need to be well-understood to estimate the quality and service life of martensitic stainless steel joints. In the present study, AISI 420 martensitic stainless steel materials were welded by using different combinations of shielding gas via the gas metal arc welding (GMAW) method. It is known that shielding gases also play a critical role in heat input, cooling rate, microstructure of weld seam, weld defects, and mechanical properties besides drying of molten weld pool. Thus, it is important to investigate the effects of shielding gases and gas combinations on the welding of martensitic stainless steels in the welding process. In the present study, 100 % Ar, 97 % Ar + 3 % H-2 and 93 % Ar + 7 % H-2 gas combinations were employed. The welded sheets were subjected to the metallographic examination as well as hardness, tensile, and bending tests. The effect of the tests and the combination of shielding gas on the mechanical and microstructural properties of AISI 420 stainless steel was investigated. The results indicated that a noticeable grain coarsening occurred in the microstructure of the weld metal and heat affected zones (HAZs) after the addition of H-2 into the Ar gas during the welding process. The highest tensile strength was obtained from the joints with 100 % Ar gas. As a result of the tensile test, rupture occurred in the base metal-HAZ transition zone in all the welded samples. In the joints welded with 97 % Ar + 3 % H-2 and 93 % Ar + 7 % H-2 gas combinations, fracture occurred in the base metal-HAZ transition zone during the bending test.