1997 年 15 巻 2 号 p. 305-313
In austenitic stainless steel weld metals solidified as ferritic single phase, subsequent ferrite-to-austenite transformation could be massive when the postsolidification cooling is rapid as in GTA welding. On the other hand, this GTA weld metal shows acicular structure of ferrite and austenite at room temperature microstructure. The effect of massive transformation on the formation of acicular structure was investigated in this study using different thermal cycle patterns and quenching technique. Massive transformation occurs below the T0 temperature within the two-phase region of ferrite and austenite at a cooling rate of approximately 100K/sec. On cooling after the massive transformation, austenite continues to grow into retained ferrite epitaxially from massive austenite while ferrite precipitates again at twin boundaries within the massive austenite. This suggests that acicular structure of ferrite and austenite is formed even if the massive transformation occur. In this case, the grain refinement and rapid progress of structure formation are expected as compared with weld metals in which massive transformation does not occur.