不锈钢热塑性降低的非平衡偏聚机理

Mintz于1997年报道了一个有趣的试验现象:随着拉伸应变速率的增加,奥氏体钢韧性降低,铁素体钢韧性反而提高。其机制未得到解释。通过计算试验钢中P原子的非平衡晶界偏聚临界时间,结果发现奥氏体钢拉伸前热过程的等效时间短于其临界时间,而铁素体钢的等效时间长于其临界时间。由于奥氏体钢和铁素体钢分别在850和800℃等效时间最接近临界时间,韧性最低,即试验钢的热塑性降低都是由于非平衡晶界偏聚的临界时间造成的。应变速率降低,弹性应力作用时间增加。晶界偏聚量改变,热塑性降低的程度也随之改变。即热塑性降低的程度随应变速率的改变是由应力引起的非平衡晶界偏聚决定。

Non-equilibrium grain boundary segregation mechanism for reduction of hot ductility of stainless steels

An interesting experimental phenomenon was founded by Mintz in 1997, that is, the hot ductility of an austenitic steel decreases with increasing strain rate while that of a ferritic steel increases. However, the mechanism of this phenomenon is now still unclear. The critical time of non-equilibrium grain boundary segregation for P in the tested steel was calculated. The results show that the effective time of the austenitic steel is shorter than the critical time while that of the ferritic steel is longer than the critical time. Because the effective time of the austenitic steel is very close to the critical time at 850?? while the effective time of the ferritic steel is very close to the critical time at 800??, the ductility achieves minimum. Namely, the reduction of hot ductility of the steels is mainly induced by the critical time of non-equilibrium grain boundary segregation. Decreasing strain rate increases elastic stress ageing time. The segregation concentration at grain boundary changes, and the degree of reduction of hot ductility also changes. Consequently, the degree of reduction of hot ductility with change of strain rate is determined by stress induced non-equilibrium grain boundary segregation.