High-Temperature Low-Cycle Fatigue Behavior of HS80H Ferritic–Martensitic Steel Under Dynamic Strain Aging

In this work, low-cycle fatigue tests were performed on HS80H ferritic–martensitic steel with the strain amplitudes ranging from 0.5 to 2.0% at room temperature and 350 °C. The cyclic stress response at 350  °C was found to be different from that at room temperature due to the effect of dynamic strain aging and showed a significant secondary hardening when the strain values were 0.5 and 0.7%. Furthermore, the dynamic strain aging effect also resulted in an abnormal increase in fatigue life when the strain was 0.7%, which was due to the change in elastic strain. Additionally, the elastic strain and fatigue life were bilinear relations in the double logarithmic coordinates. Finally, the transmission electron microscope observations showed that the dynamic strain aging led to the change in substructure, while the grain was refined.