凝固モードに対するレーザ急冷凝固処理の影響

ステンレス鋼のレーザ表面改質に関する研究(第1報)

抄録

In this study, a series of Fe-Cr-Ni ternary alloys were treated by CO₂ laser surface melting and effects of rapid solidification on solidification modes and microstructures were investigated. It was found that two new type solidification modes; rod-like eutectic mode and massive solidification mode, occurred in laser surface melted alloys in addition to the four types observed in conventional welding metals. The rod-like eutectic solidification formed in the compositional range in which primary ferrite solidification occurs in TIG welding metals with iron content of less than 65%. The compositional range of rod-like eutectic first increased and then decreased a little with increasing cooling rate. It was also shown that massive solidification took place only at a small compositional range in which primary ferrite solidification occurs in TIG welding metals but iron content is larger than 65%, when a critical cooling rate was achieved. The solidification modes can be classified into six types in laser surface melted alloys. With increasing cooling rate it changed. largely depending onto compositions of alloys. For the experimental conditions of present study, six kinds of changes in solidification mode were seen as shown below: (1) full austenite to full austenite, (2) primary austenite to full austenite, (3) primary ferrite to primary austenite to full austenite, (4) primary ferrite to rod-like eutectic to full austenite or massive solidification mode, (5) primary ferrite (to full ferrite) to massive solidification mode, and (6) full ferrite to full ferrite.