Microstructure of Heat-Affected Zone in High-B 9Cr Steels
Phase transformation during welding process makes fine grains in HAZ of 9Cr steels.It results in premature failure, i.e., type Ⅳ fracture, under high temperature creep conditions.However, NIMS dcvelopcd high B-9Cr steel and showed that B addition and N reduction inhibit grain refinement after welding and prolong the creep lifetime.That leads to (1) B segregation in M23C6, which has higher pinning effect than MX, near prior anstenitc grain boundaries and (2) lack of MX which is nucleation site ofα phase.Because of those, grain boundary migration with phase transformation is suppressed in high-B 9Cr steel, and then the steel shows higher Ac3 point than the Gr.92 steel.In conclusion, this study suggests that designing stabilized M23C6 and cutting the amount of MX forms a superior welded microstructure and results in a longer creep lifetime than the conventional 9Cr steels.
High B-9Cr steel M23(B,C)6 MX Phase transformation Weld joint
Tetsuya Matsunaga Masaaki Tabuchi Hiromichi Hongo Ryoji Sahara
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047.Japan
国际会议
长沙
英文
89-92
2016-10-16（万方平台首次上网日期，不代表论文的发表时间）