Low cycle fatigue behavior and failure mechanism of a dual-phase steel

Low cycle fatigue behavior and failure mechanism of a dual-phase steel was investigated by using LCF tests, interrupted LCF tests, SEM, TEM and XRD peak broadening. LCF tests were performed at constant strain amplitudes of ±0.002, ±0.004, ±0.006 and ±0.1. Microscopic investigations were carried out on gauge surfaces of the interrupted LCF specimens at various stages of their fatigue life. It was observed that at high strain amplitudes damage was started at fractured martensite particles and passed through areas with high density of martensite. At low strain amplitudes damage was started at separated ferrite/martensite interface and passed through areas with low density of martensite. All specimens showed fatigue hardening during LCF tests. It was also observed that the rate of hardening was affected by strain amplitude. The results show that XRD peak broadening is sensitive to the strain amplitude and the stage of damage in the specimens.