1991 Volume 9 Issue 4 Pages 501-506
The penetration in GTA welding is affected by the fluid flow in molten pool, and the fluid flow is profoundly influenced by the minor elements in base metal such as sulfur, oxygen and chlorine. The purpose of this work is to make clear the mechanism of the minor element effect on the fluid flow in metal pool.
As described in the previous paper, the anode size on arc weld pool is sensitive to the minor element in base metal. This means that the electro-magnetic force is one of the important factors for the minor element effect in arc weld pool.
In the present work, a defocused electron beam has been used as a heat source to discuss the influence of the element on the surface tensional convection.
The results of the present work are summarized as follows,
(1) The fluid flow pattern in the pool by a defocused electron beam is dependent on the evaporation process in molten pool.
(2) Under the condition of high evaporation rate, the metal flow on the pool surface, induced by the frictional force of evaporation jet, is outward from the center of the molten pool.
(3) Under the condition of low evaporation rate, where the frictional force due to the jet is negligible, the fluid flow is inward along the pool surface toward the center.
(4) The sulfur in base metal depresses the metal vaporization from molten pool.
(5) The ratio of sulfur content in the pool decreases during evaporating, i.e., the sulfur element evaporates predominantly from the pool surface.
(6) The above result suggests that a surface tensional gradient on molten pool surface due to the evaporation of surface active element (sulfur) is important as the mechanism of the inward flow on pool surface.