两相区保温过程中9Ni钢组织的演化及其对钢性能的影响

Evolution of Microstructure During Holding Process at Two Phase Region and Its Effect on Properties of 9Ni Steel

使用热膨胀仪测定了两相区保温过程中9Ni钢试样尺寸的变化,进而根据膨胀量的变化理论计算了两相区保温不同时间时钢中的奥氏体含量,并结合SEM组织观察,分析了两相区保温期间奥氏体量的变化规律及其对9Ni钢低温韧性的影响。结果表明:在保温初始阶段,奥氏体量快速增加,10 min即达到56.7%左右,此后增加趋势逐渐减缓,超过30 min后则趋于稳定,此后再延长保温时间主要发生原生马氏体的再结晶及奥氏体晶粒的粗化,使得组织中的大角度晶界减少,不但使钢强度降低,且低温韧性也恶化,因此两相区保温时间不应超过30 min。

Thermal dilatometer was used to determine the size change of 9Ni steel which was heated in two-phase region and held for different time. The content of austenite in the steel was obtained by theoretical calculation according to the results of thermal expansion, and then the change of anstenitic content in the steel held for different time in two phase region and its effects on properties of 9Ni steel were discussed. The results show that the austenitic content increases sharply at the beginning of insulation, it reaches 56.7% after holding for 10 min, then increases slowly and tends to be a constant after holding for 30 min. Therefore, the recrystallization of the quenching martesite and the growth of the austenite grain obtained in two phase region are enhanced when holding for too long time, and the large angle grain boundaries decrease gradually, which leads to the reduction of strength and the deterioration of low temperature toughness. For the 9Ni steel is treated by QLT, its holding time in two phase region should not exceed 30min.