不同控制模式下316L不锈钢的高温疲劳变形行为及寿命预测

High Temperature Fatigue Deformation Behavior and Life Prediction of 316L Stainless Steel under Different Control Modes

在550℃下对核电用316L不锈钢进行应变控制(应变幅在0.3%~1.2%)、应力控制(应力幅在230~300 MPa)低周疲劳试验和应变控制蠕变疲劳试验(3种波形,拉伸保载60,180,600 s,压缩保载60,180 s,拉压对称保载180 s),通过疲劳寿命、循环响应特征和应力-应变滞回曲线分析了不同控制模式下试验钢的疲劳变形行为;构建疲劳寿命预测模型,评估了Manson-Coffin-Basquin模型、SWT模型和能量法模型对不同控制模式下试验钢疲劳寿命的预测能力。结果表明:在不同控制模式的疲劳循环载荷下,316L不锈钢的循环应力响应均包括循环硬化、循环软化和失效断裂3个阶段;在低周疲劳试验中,疲劳寿命随应变幅或应力幅的增大而缩短;在蠕变疲劳试验中,疲劳寿命随拉伸保载时间的延长而缩短,随压缩保载时间的延长而增大,这与动态应变时效和蠕变对疲劳损伤的综合作用有关;在相同保载时间下,压缩保载下的疲劳寿命比拉伸保载下的短,这与不同加载方向引起的氧化层致裂机制有关。能量法模型对316L不锈钢在不同控制模式下的疲劳寿命预测精度最高,预测精度在1.5倍误差带以内,Manson-Coffin-Basquin模型的预测精度最低。

Strain controlled(strain amplitude of 0.3%-1.2%)and stress controlled(stress amplitude of 230-300 MPa)low cycle fatigue tests,and strain controlled creep fatigue tests(three waves including tensile holding for 60,180,600 s,compressive holding for 60,180 s and tensile and compressive symmetric holding for 180 s)at 550℃were conducted on 316L stainless steel for nuclear power.The fatigue deformation behaviour of the test steel under different control modes was analyzed through fatigue life,cyclic response characteristics and stress-strain hysteresis curves.The fatigue life prediction models including Manson-Coffin-Basquin model,SWT model,and energy method model were constructed and the predictive ability of these models for fatigue life of the test steel under different control modes was evaluated.The results show that the cyclic stress response of 316L stainless steel included cyclic hardening,cyclic softening and failing fracture stages under fatigue cyclic load of different control modes.In the low cycle fatigue test,the fatigue life decreased with the increase of strain or stress amplitude.In the creep fatigue test,the fatigue life decreased with the extension of tensile holding time and increased with the extension of compressive holding time,which was related to the comprehensive effect of dynamic strain aging and creep on fatigue damage.Under the same holding time,the fatigue life under compressive holding was shorter than that under tensile holding,which was related to the cracking mechanism of oxide layer caused by different loading directions.The energy method model had the highest accuracy in predicting the fatigue life of 316L stainless steel under different control modes,with prediction accuracy within 1.5 times the error band,and the Manson-Coffin-Basquin model had the lowest prediction accuracy.