回转奥氏体对9Ni钢低温断裂机制的影响

Effect of reversed austenite on low temperature fracture mechanism of 9Ni steel

采用示波冲击法测定了9Ni钢冲击过程中裂纹萌生、扩展等阶段所消耗的能量,并通过测定钢中回转奥氏体含量,研究了冲击断裂过程中回转奥氏体的作用机制。结果表明:随着回转奥氏体含量的增加,裂纹形核功不断上升,但趋势减缓,而裂纹扩展功则先快速上升后又大幅下降,峰值与回转奥氏体稳定性的峰值重合,表明稳定性差的回转奥氏体会导致扩展功大幅下降。由于裂纹形核功随回转奥氏体稳定性的变化相对平缓,扩展功的变化则更为剧烈,因此提高回转奥氏体稳定性进而增加扩展功是改善9Ni钢低温韧性的有效手段。

The energy absorbed during initiation and propagation of crack in impact fracture process of a 9Ni steel was obtained by instrumented impact tests,and the amount of reversed austenite was also measured by XRD,then the mechanism of reversed austenite in fracture process was studied. Results show that the nucleation energy of crack increases with the increasing of reversed austenite,but the trend slows down. Propagation energy increases obviously and reaches the peak value when the reversed austenite achieves the maximum stability,then decreases sharply,which indicates that unstable reversed austenite can cause the decreasing of propagation energy even its amount is raised. The results also show that,compared with initiation energy,change of propagation energy with the stability of reversed austenite is more remarkable,so the most effective method to improve the cryogenic toughness of 9Ni steel is to increase the propagation energy by obtaining the reversed austenite with high stability.