AbstractThe levitating–drop method has been used to determine surface tension as a function of temperature for four transition metals, and also for samples of type 316 stainless steel which exhibited variable weld penetration during tungsten-inert-gas welding. The results obtained verify the predictions of weld-pool models in that the differences in weldability of the steels can be related to the surface properties of the melts. To obtain good weldability in type 316 steels, it is necessary to ensure that the concentration of uncombined surface-active elements (such as sulphur) should exceed a specified minimum level. An indication of the amounts required for consistent weld penetration is given.MST/194