热处理对9Ni钢组织和深冷韧性的影响

Effects of heat treatment on microstructure and cryogenic toughness of 9Ni steel

采用SEM,TEM,XRD等方法研究了9Ni钢经两相区热处理(QLT)和调质处理(QT)后的精细组织,奥氏体含量,深冷冲击韧性和断口。结果表明,QLT处理有利于生成奥氏体。两相区加热温度TL为660℃时,试验钢中奥氏体的体积分数为12.2%,-196℃下的夏比冲击吸收能量为148 J。经QT处理的试样含有较高的位错密度,且伴有碳化物析出,冲击韧性降低。断口分析表明,QLT处理试样为等轴韧窝断裂特征,而QT处理试样为河流状解理断裂特征。示波冲击试验表明,QLT试样失稳断裂时,产生大量塑性变形,断裂吸收能远大于QT处理试样。

Microstructure, volume fraction of austenite, cryogenic toughness and fracture morphologies of 9Ni steel under QLT and QT heat treatment were investigated by SEM, TEM and XRD. The results show that QLT treatment facilitates the precipitation of austenite. When the heating temperature of two-phase region （ TL） is 660 ℃ ,the volume fraction of austenite is 12.2%, Charpy impact absorption energy of QLT sample reaches 148 J at - 196 ℃. The microstructure of the steel treated by QT has high density of dislocations and precipitated carbides, which deteriorate the toughness. The fracture of QLT treated sample is featured by equiaxed dimples while QT sample is mainly river pattern cleavage. The difference in toughness of the two heat treating samples is the absorbed fracture energy. During unstable fracture, QLT treated sample occurs a lot of plastic deformation, and the absorbed energy is significantly higher than that of QT treated sample.