1999 年 17 巻 3 号 p. 387-396
The effect of chemical compositions on anode area formation in tungsten inert gas arc welding was investigated to clarify the influence of alloying elements on the weldability of high alloyed steels in fabrication. Welding tests were carried out on 25%Cr- 22%Ni stainless steel plates with various amounts of surface active elements, manganese, silicon and aluminum. In these welding tests, the molten pool surface was observed using a high-speed video camera and spectrum analysis of arc plasma was done by using a spectroscope. Chemical composition of welding fumes was also analyzed. The results showed that the size of the anode area and the direction of the molten metal flow were influenced only by surface active elements. The slag containing manganese was observed in the quenched molten pool surface and the size of the distribution area of the slag corresponded closely to the size of the anode area. Based on the results of spectrum analysis of the arc plasma and chemical analysis of the welding fumes, the mechanism of anode area formation is considered to be as follows. Manganese is vaporized from slag carried by the molten metal flow and ionized in the arc column. Consequently, the anode area is formed on the slag gathered area that is a conduction path of arc current. Therefore, the size of anode area appears to be determined by surface active elements because they influence the direction of the molten metal flow.