22Cr15Ni3.5CuNbN stainless steel is a newly developed heat-resistant austenitic steel for superior ultra-super critical fossil power plants with operating temperature up to 650 °C. In this study, low cycle fatigue (LCF) behavior and fatigue failure damage mechanism of this steel were investigated. The LCF tests were conducted at 650 °C in air. The microstructures, dislocations and precipitates after the LCF were studied to identify the fatigue damage mechanism. A cyclic hardening behavior was observed, where the cyclic hardening rate increased first and deceased as the applied strain amplitude was greater than 0.50%. This was similar to the variation of the dislocation density. A high strain amplitude induced dislocation annihilation and thus the cyclic hardening rate of 0.60% strain amplitude became lower than that of 0.50%. In addition, dynamic strain ageing occurred and depended on the plastic deformation and in the case of low strain amplitude it gradually disappeared after a few cycles while in the case of high strain amplitude it maintained through the fatigue life. Moreover, the fatigue cracks initiated at the outer surface and mainly in grain boundaries, twin boundaries and triple grain boundaries, owing to the high strain localization and the strong interaction between dislocations and precipitates.

22Cr15Ni3.5CuNbN不锈钢是一种新开发的耐热奥氏体钢，用于工作温度高达650°C的超超临界火力发电厂。在这项研究中，研究了该钢的低周疲劳（LCF）行为和疲劳破坏损伤机理。LCF测试在650°C的空气中进行。研究了LCF后的微观结构，位错和析出物，以确定疲劳损伤机理。观察到循环硬化行为，其中循环硬化率首先增加，并且随着施加的应变幅度大于0.50％而降低。这类似于位错密度的变化。高应变幅度引起位错an灭，因此0.60％应变幅度的循环硬化率低于0.50％。此外，动态应变老化发生并取决于塑性变形，在低应变振幅的情况下，它会在几个周期后逐渐消失，而在高应变振幅的情况下，它会维持整个疲劳寿命。此外，由于高应变局部化和位错与析出物之间的强相互作用，疲劳裂纹始于外表面，主要出现在晶界，孪晶界和三晶界。