Effect of sulfur and oxygen on weld penetration of high-purity austenitic stainless steels

Convective flow during arc welding depends upon the surface tension gradient (dy/dT, Marangoni flow), buoyancy, arc drag force, electromagnetic force, shielding gas, and the viscosity of the melt. The Marangoni and the buoyancy-driven flow are the major factors in controlling weld penetration in ferrous alloys, especially austenitic stainless steels such as 304 and 316. Small variations in the concentration of surfactants, such as sulfur and oxygen, in stainless steels cause significant changes in the weld penetration and depth/width (D/W) ratio of the fusion zone. Gas-tungsten arc (GTA) welds were done on low- and high-sulfur 304 and 316 heats using pure argon and argon/oxygen shielding gases. Also, laser beam (LB) welds were done on the 304 and 316 heats using pure argon as the shielding gas. Increase in the sulfur content decreased the D/W ratio for the GTA 304 welds using pure argon, but for the case of LB 304 welds the results were the opposite. For the GTA 316 welds and LB 316 welds, increase in sulfur increased the D/W ratio of the fusion zone. Oxygen increased the D/W ratio of both the 304 and 316 GTA welds.