显微组织对P92钢蒸汽管道焊缝区蠕变裂纹扩展速率的影响

Effect of Microstructure on Creep Crack Growth Rate in Welding Seam of Hot Reheat Steam Pipe Made of P92 Steel

采用光学显微镜、扫描电镜和透射电镜对1000 MW超超临界发电机组P92钢再热蒸汽管道焊缝区的显微组织及其对蠕变裂纹扩展速率的影响进行了深入的研究。结果表明,试验用P92钢蒸汽管道焊缝区为回火马氏体组织,其组织极不均匀,主要表现在马氏体的回复程度相差较大。马氏体回复程度越低,板条形态保持得越好,板条越细密,蠕变裂纹扩展速率就越小。在焊缝区,原奥氏体晶界、马氏体板条界及亚晶界上主要分布有两种析出相,即富含钨、钼的Laves相和富含铬的M_(23)C_6型碳化物;而在焊缝区晶体内部除有上述两种析出相外,还有富含钒、铌的MX型碳化物,且Laves相总伴生在M_(23)C_6型碳化物处。

The effect of microstructure on creep crack growth rate in welding seam of hot reheat steam pipe made of P92 steel was studied. The results show that the representative microstructure of the investigated welding seam is tempered martensite, but the recovery extent of lath martensite structure in distinct zones is different. The lower the recovery extent of lath martensite structure and the smaller the lath width of martensite, the smaller the creep crack growth rate. There exist two kinds of precipitates on the boundaries of prior austenite grains, martensite laths and subgrains, namely Laves phase and M23C6 carbides,whereas in grain interiors,there is also MX carboniterides besides Laves phase and M23C6 carbides and the Laves phase is almost always tied up to the M23C6 particles.