Effect of Work-Hardening Mechanisms in Asymmetrically Cyclic-Loaded Austenitic Stainless Steels on Low-Cycle and High-Cycle Fatigue Behavior

Dislocation characteristics and deformation-induced martensite (DIM) transformation in an asymmetrically cyclic-loaded metastable type 304 stainless steel (SS) are investigated compared with a stable type 316SS using EBSD and X-ray diffraction line-profile analysis. In low-cycle fatigue (LCF) regime, differences between dislocation densities of type 304SS and type 316SS are increased with decreasing fatigue life, and contribution of alpha '-martensite to work hardening of cyclically loaded type 304SS increased with decreasing fatigue life. However, the contribution of austenite slightly changed. Higher work hardening via DIM transformation improves the fatigue life of type 304SS than that of type 316SS in LCF regime in the same fatigue stress amplitude. Thus, the contribution of alpha '-martensite to work hardening is a determinant parameter, affecting the fatigue behavior of type 304SS. In HCF regime when the alpha '-martensite had a small contribution to the work hardening, the fatigue life of type 304SS is slightly higher than that of type 316SS.