在现有研究中，低活化9Cr-ODS钢虽然具有优异的高温性能，但其低周疲劳性能及微观组织演变规律尚未全面揭示，本工作旨在揭示其在不同应变幅下的循环响应和裂纹扩展特性。采用应变控制测试方法，研究了低活化9Cr-ODS钢在0.3%~0.8%应变幅范围内的室温低周疲劳性能，包括循环应力响应曲线、滞后回线、应变幅与寿命以及应力幅与塑性应变的关系，给出了相应的疲劳参数，并分析了疲劳过程中微观组织演变、疲劳断口形貌及裂纹扩展特性等。结果表明，9Cr-ODS钢的循环应力响应行为与应变幅有关。随应变幅增加，材料的峰值拉应力增加，疲劳寿命降低，循环应变-寿命满足Coffin-Manson关系。9Cr-ODS钢在所有应变幅下未出现明显的循环硬化，但在0.5%~0.8%较高应变幅范围内发生了一定的循环软化。微观组织分析表明，随循环应变幅增加，亚结构发生了回复，位错密度降低，平均晶粒尺寸及大角度晶界占比逐渐增加，从而导致9Cr-ODS钢的循环软化。疲劳裂纹起源于样品表面，但裂纹源附近均未发现明显的夹杂物或析出相。裂纹以穿晶方式扩展，9Cr-ODS钢细的原始奥氏体晶界及亚晶界对裂纹扩展具有强烈的抑制作用。此外，在相同低应变幅且不降低循环疲劳寿命条件下，9Cr-ODS钢所能承受的峰值拉应力达到低活化铁素体/马氏体钢的2倍，显示出较优越的低周疲劳强度。

Adequate studies have not been conducted on the low cycle fatigue properties of oxide dispersion strengthened (ODS) steels that are typically used for fusion reactors worldwide. Moreover, the majority of the fatigue properties are examined with a small sample size due to the restricted manufacturing capacity, which is insufficient for determining the comprehensive properties of bulk materials. Research on the fatigue properties of Chinese ODS steels was conducted recently. However, it is quite uncommon to report the fatigue properties of self-produced 9Cr-ODS steel. Consequently, this work is the first to examine the effect of a cyclic strain on the low cycle fatigue behavior of a representative low-activation 9Cr-ODS martensitic steel. Hence, the strain control test method was employed here in a strain amplitude range of 0.3%-0.8% at room temperature. The cyclic stress response curves, hysteresis loops, relationships between strain amplitude and life, stress amplitude and plastic strain were obtained, and the corresponding fatigue parameters were summarized. Furthermore, the microstructural evolution, fatigue fracture morphology, and crack propagation characteristics during the fatigue process were analyzed. The results revealed that the cyclic stress response behavior of the 9Cr-ODS steel was related to the strain amplitude. With an increase in the strain amplitude, the peak stress in the tension zone of 9Cr-ODS steel increased and the fatigue life decreased. The relationship between cyclic strain and life agreed well with the Coffin-Manson model. Additionally, the 9Cr-ODS steel had no obvious cyclic hardening but revealed a cyclic softening under higher strain amplitudes of 0.5%-0.8%. The microstructure analysis showed that for higher cyclic strain amplitudes, the average grain size and the fraction of the large-angle grain boundaries increased gradually with a reduction in the dislocation density, leading to the cyclic softening of the material. The fatigue crack initiated at the surface and propagated inward by the transgranular mode. The fine grain boundaries and subgrain boundaries of the 9Cr-ODS steel could induce crack deflection, reduce crack propagation rate, and increase fatigue crack propagation life. Moreover, under the same strain amplitude, the peak stress in the tension zone of the steel was almost twice that of the China low activation martensitic (CLAM) steel without a reduction in the fatigue life, indicating a superior low cycle fatigue resistance of the 9Cr-ODS steel.