Abstract
The penetration in GTA welding is affected by the convective fluid flow in molten pool and the fluid flow is strongly influenced by the minor elements such as sulfur, oxygen and chlorine in base metal. The purpose of this work is to make clear the mechanism of the minor element effect on the fluid flow in GTA welding.
In the first, the influence of the element on anode configuration on molten pool surface has been discussed experimentally under the condition of He-shielding, where the anode mode can be observed clearly. As the result of the experiment, it is made clear that the anode size is very sensitive to the elements and these elements such as sulfur, oxygen and chlorine depress the evaporation of metal vapor from the molten pool surface and make the anode zone constricted.
In the second part of this paper, a defocused electron beam has been used as a heat source to discuss the influence of the minor element on the surface tensional convection, i.e. the influence of sulfur content in base metal on the penetration by the defocused electron beam has been discussed. It is clarified that the penetration shape by defocused electron beam is insensitive to the sulfur content in base metal. This result of electron beam melting, where the electromagnetic force is negligible as the driving force of covection, suggests that the minor element effect is peculiar to arc weld pool.
From these experimental results, the minor element effect may be explained as follows, the element influences the anode size on molten pool surface and it causes the change of fluid flow mode in molten pool, because the convective flow by electro-magnetic force is directly dependent on the anode size.
