Effect of high temperature on crack initiation of super austenitic stainless steel 654SMO in very high cycle fatigue

Working service of structural materials at elevated temperatures generally leads to a significant decrease in their fatigue performance, thereby threatening the safety and reliability of engineering structures. In this pursuit, the very high cycle fatigue behavior and the relevant crack initiation mechanism of super austenitic stainless steel 654SMO was comparatively investigated at room temperature (RT) and high temperature (HT, 300 degrees C). It was found that the heterogeneous microstructure strongly influenced the fatigue failure mechanism, wherein the crack initiation sites transferred from fine grain clusters at the RT to coarse grains at HT. Furthermore, the cross-section of the crack initiation sites revealed that the micro-porosity and accumulative slip bands resulted in the crack originations at RT and HT, respectively. The differences of crack initiation were ascribed to the effect of elevated temperature, which weakened the sensibility of crack initiation to micro-defect in very high cycle fatigue regime. Our study provides new insights in the correlation of high temperature and heterogeneous microstructure, in regards to the crack initiation behavior. (C) 2020 The Authors. Published by Elsevier Ltd.