对汽轮机用3.5NiCrMoV贝氏体钢和20Cr13马氏体钢进行对称和非对称应变控制疲劳试验，对比研究其疲劳行为；采用基于对称应变疲劳参数的Morrow模型、SWT模型和Ellyin模型对非对称疲劳寿命进行预测，讨论模型的适用性。结果表明：3.5NiCrMoV钢的非对称疲劳寿命不高于对称疲劳寿命，20Cr13钢的非对称疲劳寿命高于对称疲劳寿命；3.5NiCrMoV钢的对称和非对称循环应力相差较大，而20Cr13钢的对称和非对称循环应力相近；平均应力下降是非对称应变控制疲劳的共同现象，塑性应变变化是影响非对称疲劳寿命的主要因素；Morrow模型预测精度取决于应变比对疲劳寿命的影响，SWT模型不适用于非对称与对称疲劳循环应力-应变曲线相差较大的3.5NiCrMoV钢疲劳寿命预测，Ellyin模型对非对称与对称循环硬化趋势相近的20Cr13钢的非对称疲劳寿命具有较好的预测效果。

Symmetric and asymmetric strain control fatigue tests were performed on 3.5NiCrMoV bainite steel and 20Cr13 martensite steel for steam turbine, and their fatigue behaviors were compared and studied. Morrow model, SWT model and Ellyin model based on symmetric strain fatigue parameters were used to predict asymmetric fatigue life, and the applicability of these models was discussed. The results show that the asymmetric fatigue life of 3.5NiCrMoV steel was not higher than its symmetric fatigue life, and the asymmetric fatigue life of 20Cr13 steel was higher than its symmetric fatigue life. There was a big difference between symmetric and asymmetric cyclic stresses of 3.5NiCrMoV steel, and the symmetric and asymmetric cyclic stresses of 20Cr13 steel were similar. The average stress reduction was a common phenomenon for asymmetric strain control fatigue, and the plastic strain change was the main factor affecting asymmetric fatigue life. The prediction accuracy of the Morrow model depended on the effect of strain ratio on fatigue life. The SWT model was not suitable for fatigue life prediction of 3.5NiCrMoV steel with a large difference between asymmetric and symmetric cyclic stress-strain curves. The Ellyin model had a good prediction effect on the asymmetric fatigue life of 20Cr13 steel with similar asymmetric and symmetric cyclic hardening trends.