EFFECT OF SULFUR AND OXYGEN ON WELD PENETRATION OF HIGH-PURITY AUSTENITIC STAINLESS-STEELS

Convective flow during are welding depends upon the surface tension gr adient (d gamma/dT, Marangoni flow), buoyancy, are drag force, electro magnetic force, shielding gas, and the viscosity of the melt. The Mara ngoni and the buoyancy-driven flow are the major factors in controllin g weld penetration in ferrous alloys, especially austenitic stainless steels such as 304 and 316. Small variations in the concentration of s urfactants, such as sulfur and oxygen, in stainless steels cause signi ficant changes in the weld penetration and depth/width (D/W) ratio of the fusion zone. Gas-tungsten are (GTA) welds were done on low- and hi gh-sulfur 304 and 316 heats using pure argon and argon/oxygen shieldin g gases. Also, laser beam (LB) welds were done on the 304 and 316 heat s using pure argon as the shielding gas. Increase in the sulfur conten t 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 GT A 316 welds and LB 316 welds, increase in sulfur increased the D/W rat io of the fusion zone. Oxygen increased the D/W ratio of both the 304 and 316 GTA welds.