Enhanced fatigue resistance of cold-drawn AISI 316L via stress relieving heat treatment promoting metastable phase transformation

Previous studies have shown that metastable phase transformation under cyclic loading can enhance the fatigue performance of AISI 316L. However, the underlying mechanisms and the potential for further improvement remain unclear. This study aims to investigate the cyclic deformation mechanisms in cold-drawn AISI 316L and the effect of stress relieving heat treatment. Cold-drawn and stress-relieved specimens were subjected to tensile and stress-controlled fatigue testing. The stress relieving heat treatment significantly improved fatigue performance while resulting in a slight increase in yield strength. Microstructural characterization revealed that this improvement can be attributed to the combined effects of increased yield strength and a greater extent of martensitic transformation in dislocation-free regions under cyclic loading, which delays fatigue crack initiation. The stress relieving heat treatment promotes the development of a low-energy dislocation configuration, which facilitates the formation of dislocation-free regions under cyclic loading and subsequently promotes martensite nucleation. Furthermore, the distribution of martensitic transformation under cyclic loading was found to differ from that under monotonic loading, primarily due to differences in dislocation arrangements under the two loading modes. This study clarifies the role of stress relieving heat treatment in fatigue resistance enhancement through metastable phase transformation and provides insights into the development of more fatigue-resistant steels.