Cyclic hardening and dynamic strain aging during low-cycle fatigue of Cr-Mo tempered martensitic steel at elevated temperatures

Dynamic strain aging (DSA) has a noticeable impact on low cycle fatigue behavior of Cr-Mo tempered martensitic steel at elevated temperatures. At 350 °C, the stress response presented evidently secondary hardening phenomenon, and the fatigue life is significantly higher than room temperature which is contrary to the usual understanding. The analysis shows that the reason for the secondary hardening is mainly because of DSA which affects the evolution of dislocations. The influence process of the DSA effect on the dislocation evolution in low-cycle fatigue was first observed, which is from lath substructure to a smaller cell substructure at high temperature. Fracture observation indicates that the new dislocation structure promotes the crack propagation resistance of the material. The effect of DSA on the low cycle fatigue properties of high temperature provides a new idea for the study of fatigue resistance of materials.