Low cycle fatigue (LCF) behavior of a tempered martensitic Fe-9%Cr-based oxide dispersion strengthened (ODS) steel at elevated temperatures is correlated to the microstructural evolution after cyclic straining. The fully reversed strain-controlled tests were conducted in air at 550 °C and 650 °C for different strain amplitude values ranging from ± 0.4% to ± 0.9%. Apart from the higher cyclic stress levels, the steel manifests complex cyclic softening which is significantly lower in comparison to that observed for similar non-ODS steels. This is due to the fact that highly stable nano-oxide particles act as persistent barriers for dislocation motion which as a consequence slows down the typical microstructural evolution realized in the conventional non-ODS steels. Upon cycling at 550 °C, microstructure exhibits only minor changes. The main modifications are in respect to the dislocations rearrangement and/or annihilation which finally result in their reduced density. At 650 °C, microstructural evolution hastens and becomes prominent mainly in nano-oxides/carbides deficient regions. Here, in addition to the reduced dislocation density, partially eliminated original sub-grain structures, grain growth, M₂₃C₆ carbides coarsening and Cr-W enriched Laves phase precipitation were evident. The microstructural modifications, concerning dislocation density and sub-grain structures, intensify even further with increase in applied strain amplitude. Nevertheless, annealing at 650 °C for similar duration has no major influence on microstructure. Damage studies revealed expeditious as well as pronounced damage with increase in applied strain amplitude. Cracks initiation, eventuates at the early stage of the test, and their propagation were further assisted by oxidation. The stable crack growth region manifests secondary cracks, and at higher magnification the classical fine-scale transgranular ductile fatigue fracture features called striations. In addition, at 650 °C, crack path also acquires an intergranular tendency under higher strain amplitude.

回火马氏体Fe-9％Cr基氧化物弥散强化（ODS）钢在高温下的低循环疲劳（LCF）行为与循环应变后的组织演变有关。在550°C和650°C的空气中进行完全反向应变控制的测试，测试范围为±0.4％至±0.9％。除了较高的循环应力水平外，该钢还表现出复杂的循环软化作用，与类似的非ODS钢相比，其显着降低。这是由于以下事实：高度稳定的纳米氧化物颗粒充当位错运动的持久屏障，因此减慢了常规非ODS钢中实现的典型微观组织演变。在550°C下循环时，微观结构仅显示微小变化。主要修改是关于位错重排和/或an灭，这最终导致其密度降低。在650°C，主要在纳米氧化物/碳化物缺陷区域，微结构的演化加快并变得显着。在这里，除了降低位错密度外，还部分消除了原始的亚晶粒结构，晶粒长大，M₂₃ ℃ ₆碳化物粗化和富Cr-W的Laves相沉淀是明显的。与位错密度和亚晶粒结构有关的微观结构改变，随着施加应变幅度的增加而进一步增强。尽管如此，在650°C下退火相似的时间对显微组织没有重大影响。损伤研究表明，随着施加应变幅度的增加，迅速而明显的损伤。裂纹的产生，在测试的早期阶段最终产生，并且裂纹的扩展进一步受到氧化的辅助。稳定的裂纹扩展区域表现出二次裂纹，并且在更高的放大倍数下，经典的细尺度跨晶系延性疲劳断裂特征称为条纹。此外，在650°C时，裂纹路径在较高的应变幅度下也具有晶间趋势。