Microstructural analysis on JLF-1 steel tested by fatigue deformation

Microstructural changed of JLF-1 steel induced by static tensile loading and tension/compression cyclic loading was investigated following tensile and low cycle fatigue tests in vacuum at elevated temperature. Secondary cracks in radial direction were observed on the fracture surface of the tensile specimen at RT. Initial cyclic hardening followed by cyclic softening was observed during fatigue at RT and 673 K. In contrast, only cyclic softening was observed at 873 K. Transmission electron microscopy images of specimens with a total strain range Δεt = 1.8% at RT, 673 K and 873 K showed that cyclic softening is caused by the reduction of the dislocation density and increment of lath width resulted by partial annihilation of original lath boundaries and cyclic deformation. The peak stress and lath width imply qualitative relationships that correlate with the number of cycles.