INFLUENCE OF SULFUR AND WELDING CONDITIONS ON PENETRATION IN THIN STRIP STAINLESS-STEEL

Welding trials and surface tension measurements have been carried out on 304 stainless steels with sulfur (S) contents between 20 and 100 pp m. Surface tension measurements, determined by the levitated drop meth od, indicated that the temperature coefficient of surface tension (dga mma/dT) changed from negative to positive values at S contents exceedi ng approximately 50 ppm. Strips with a thickness of approximately 1 mm were GTA welded on both single-electrode, small-scale and multi-elect rode industrial-scale units. Welding speeds of 1 to 2 m min-1 were use d on the small-scale unit and up to 5 m min-1 on the industrial unit. The weld penetration was found to increase, for both full and partial penetration welds, with 1) increasing sulfur contents; and 2) increasi ng linear energy (i.e., current x voltage/welding speed). On the small scale-unit markedly higher penetration was observed in heats with S c ontents > 60 ppm. But the influence of S contents was only of minor im portance for welds obtained on the industrial unit. It was found that the similar weld geometry could be obtained for both low (less-than-or -equal-to 60 ppm) and high (> 60 ppm) sulfur contents by careful adjus tment of welding parameters. The observed changes in weld geometry are consistent with the proposition that the fluid flow in the weld pool is dominated by thermocapillary (Marangoni) forces during the GTA weld ing of thin strips.