通过拉-压对称的应变控制模式,在相同温度循环和不同应变幅(0.7%~1.1%)下对SDYZ热作模具钢进行热机械疲劳试验,研究了不同应变幅下的应力-应变滞后回线、循环应力响应曲线以及显微组织变化。结果表明:应变幅越大,试验钢的热机械疲劳应力-应变滞后回线包围的面积越大,试验钢的损伤越严重,疲劳寿命越短;热机械疲劳循环软化过程可分为初始不稳定、连续软化和失效3个阶段。热机械疲劳试验后,试验钢显微组织中的马氏体和碳化物粗化,且随着应变幅的增加,马氏体和碳化物粗化程度降低;随着应变幅的增加,疲劳裂纹的长度和宽度变大。

The thermo-mechanical fatigue test of SDYZ hot-working die steel was carried out under the same temperature cycle and different strain amplitudes (0.7%-1.1%) by the strain control mode of tension-compression symmetry. The stress-strain hysteresis loop, cyclic stress response curve and microstructure change under different strain amplitudes were studied. The results show that the larger the strain amplitude, the larger the area surrounded by the thermo-mechanical fatigue stress-strain hysteresis loop of the test steel, the more serious the damage and the shorter the fatigue life of the test steel. The thermo-mechanical fatigue cyclic softening process could be divided into three stages of initial instability, continuous softening and failure. After the thermo-mechanical fatigue test, the martensite and carbides in the microstructure of the test steel were coarsened, and the coarsening degree of martensite and carbides decreased with increasing strain amplitude. With the increase of strain amplitude, the length and width of fatigue cracks increased.