Effect of liquid metal environment on nucleation of fatigue cracks in an austenitic stainless steel

The compatibility of nuclear materials in contact with Generation IV reactor coolants such as lead‑bismuth eutectic (LBE) still requires experimental justification. One of the key mechanical properties is fatigue life, both for reactor design and for life extension programmes. In this work, the characteristics of surface cracks in austenitic stainless steel 316 L was analysed after low cycle fatigue tests at 350 °C in three different environments: air, vacuum, and LBE. The density and length of nucleated fatigue microcracks was characterized for the different environments. Compared to tests in vacuum, a large number of shallow microcracks were found in the LBE environment, while fewer but significantly deeper cracks were observed in air. Finite element calculations were performed to estimate the impact of the different crack depths and densities on the stress behaviour of the material. The large crack density found in LBE had negligible impact on fatigue life when compared to air, and fatigue lives were comparable. Furthermore, due to their shallow nature, the cracks in LBE resulted in a stress response behaviour closer to the absence of environment than the deeper air cracks, which produce an apparent softening of the material during cyclic loading.