Low-cycle fatigue properties of 800 MPa-grade ultrafine-grained steel

The low-cycle fatigue test of 800 MPa-grade ultrafine-grained HSLA was done. The result showed that the low-cycle fatigue cycle characteristic of the material is cyclic softening under the experimental condition and the softening velocity increases with the increasing of strain amplitude. Observations of the fatigue fractography revealed that fatigue cracks start from the material surface and distribute along the fracture border, which have multi-fatigue origins.