Microstructure evolution and crack propagation of 316L stainless steel under cyclic shear fatigue at different strain ratios

Abstract

This study systematically investigates the cyclic shear fatigue behavior of 316L austenitic stainless steel under varying strain ratios. A custom-made twin-bridge fatigue shear testing machine was used to conduct cyclic experiments on the material under strain-controlled conditions (1 %–4 %) withstrain ratios (R = −1, 0, 0.5). The experimental results show that, as the strain ratio increases, the maximum positive stress of the material increases under the same strain amplitudeAnalysis of the cyclic softening coefficient indicates that cyclic softening is more pronounced at low strain amplitudes. Microstructural analysis using Electron Backscatter Diffraction (EBSD) techniques shows grain refinement and increased dislocation density in 316L austenitic steel after cyclic loading, and an increase in the strain ratio leads to a higher proportion of highly deformed grains. Additionally, during crack evolution, we observed the presence of martensitic phase transformation was observed, which caused cracks to propagate along grain boundaries. These findings not only enhance the understanding of the fatigue behavior of 316L stainless steel but also provide theoretical support for its application in high-demand fields, such as nuclear power. This research offers valuable insights for the future optimization in fatigue performance and material design of austenitic stainless steels.