Room-temperature low-cycle fatigue(LCF) tests were conducted on the domestic Incoloy 800H alloy

which is utilized for the steam generator heat transfer tubes of China's first high-temperature gas-cooled reactor(HTGR) nuclear power unit. The tested specimens include those in the as-received state and those aged at 675 ℃ for 10 000 h. Moreover

the microstructure and fatigue fracture morphology of the 800H alloy were observed using a field emission scanning electron microscope(SEM). The results indicated that the room-temperature LCF properties of the Incoloy 800H alloy in both states complied with the Manson-Coffin equation. Compared with the as-received alloy

the fatigue life of the aged alloy was prolonged by 35%～56%. This improvement was associated with the precipitation of fine second phases during aging

which led to an increase in material strength. In the strain amplitude range of 0.4%～1.0%

both the as-received alloy and the aged alloy were found to follow the sequence of cyclic hardening

cyclic softening

and cyclic stabilization. Fatigue cracks were observed to initiate preferentially from the surface defects of the specimens and propagate transgranularly.