1999 年 17 巻 3 号 p. 397-402
The effect of chemical compositions on the penetration ratio and the uniformity of bead width in tungsten inert gas arc welding was investigated from the point of view of the effect of alloying elements on the behavior of the molten pool and the anode area. Welding tests were carried out on 25%Cr -22%Ni stainless steel plates with various amounts of sulfur, manganese and silicon. The penetration ratio and the uniformity of bead width were evaluated by measuring bead depth and width. Additionally, in order to evaluate the stability of the molten pool, it was observed using a high-speed video camera during welding. The penetration ratio was increased by the addition of sulfur and manganese. Silicon had no influence on penetration ratio. The uniformity of bead width was deteriorated by increasing the sulfur content but not influenced by increasing the others. This deterioration was caused by the instability of the molten pool, which increased in proportion to the shrinkage of the anode area caused by the increase of sulfur content. The increase of penetration is thought to be caused by : (1) the concentration of arc energy resulting from the anode area shrinkage, which is induced by the molten metal flow to the molten pool center driven by sulfur ; and (2) the increase of energy density resulting from vaporized manganese.