Modeling the Effect of Surface Active Elements on Weld Pool Fluid Flow, Heat Transfer and Geometry.

摘要

The influence of sulfur on the heat flow and fluid flow and the transient development of the weld pool was quantitatively evaluated for two heats of Type 304 stainless steel containing 90 and 240 ppM sulfur, respectively. A transient heat transfer model was utilized to simulate the heat flow and fluid flow in the weld pool during stationary laser and gas tungsten arc (GTA) spot welds. A recently developed surface tension model was utilized to calculate the temperature coefficient of surface tension (d gamma /dT) as a function of temperature and sulfur content. This allows a realistic evaluation of the effect of surface-active elements on the fluid flow and weld geometry. The computed results indicate that during stationary welding, the weld pool surface temperatures are fairly high. As a consequence, the temperature coefficient of surface tension becomes negative and a radially outward or a bifurcated flow of weld metal occurs even when the weld pool contains a significant amount of sulfur. The predictions of the model were verified by comparing the calculated and experimentally observed fusion zone geometry. The results indicate very good agreement between the predicted and experimentally observed fusion zone geometry, for both laser and gas tungsten arc (GTA) spot welds, due partly to the accurate treatment of surface tension gradient driven flows. 21 refs., 7 figs., 2 tabs. (ERA citation 14:028733)