Effects of low-cycle fatigue on static mechanical properties, microstructures and fracture behavior of 304 stainless steel

A series of experiments, including constant amplitude low-cycle fatigue tests, post-fatigue tension to failure tests, LOM (TEM) observations, and SEM examinations, were performed at room-temperature to investigate the effects of low-cycle fatigue damage on the static mechanical properties, microstructures and fracture behavior of 304 austenitic stainless steel. The changing characteristics of various static mechanical property parameters, including the strength parameters (σys and σult), stiffness parameter (E), ductility parameters (δ and φf) and strain hardening exponent (n) during fatigue damage process of the stainless steel were obtained experimentally and their micromechanisms were discussed by analyzing both the deformation microstructures and the fracture features of cyclically pre-deformed specimens. It was shown that the austenite/martensite transformation resulting from the accumulation of cyclic plastic strain was mostly responsible for the variation in the strength, ductility and strain hardening ability of the stainless steel during fatigue damage process. The depletion of the inherent ductility in the material due to fatigue damage evolution led to the ductile-to-brittle transition (DBT) in the fracture modes. Based on the macro/micro-experiments regarding the exhaustion of the ductility during fatigue damage, the ductility parameter was suggested as a damage indicating parameter for the present stainless steel in further studying the fatigue damage mechanics model as well as the residual fatigue life prediction method.