View article

The published literature on variable weld penetration has been reviewed and evaluated, with particular respect to autogenous TIG and laser welding processes. It was concluded that the Heiple-Roper theory provides a satisfactory explanation for variable weld penetration, namely, that the direction and the strength of the fluid flows in the weld pool caused by Marangoni convection are responsible for the large differences in weld penetrption observed with different casts. The strength and direction of these flows are determined by the sign and the magnitude of the temperature coefficient of the surface tension dγ/d T. The sign of dγ/d T is determined by the concentration of specific surfactants (S,O, and Se), in the metal, e.g. dy/d T is negative when S < 50 ppm and positive when S > 70 ppm. However, reactive elements such as AI, Ca, and Ce can have an adverse effect on penetration by reducing the soluble sulphur …