Investigation of the Influence of Grain Size on the Oxidation and Corrosion Characteristics of 316L Stainless Steel in Static Liquid Lead–Bismuth Eutectic Environment at 500°C

This study systematically investigated how grain size affects the oxidation and corrosion behavior of 316L austenitic stainless steel when exposed to liquid lead–bismuth eutectic (LBE) at 500°C. The corrosion conditions were examined across a range of grain sizes, from 1.4 ± 0.33 to 98.6 ± 5.56 μm. The tests revealed that fine‐grained microstructures exhibited significantly accelerated degradation rates, with an internal oxidation depth that was 79% greater than that of coarse‐grained microstructures. Detailed transmission electron microscopy analysis confirms that grain boundaries act as preferential diffusion paths for oxygen and metal elements. Significant differences in grain boundary density directly induce variations in the internal oxide layer structure of 316L stainless steel, where the quantity and volume fraction of Fe–Ni‐rich phases directly determine the inability of the internal oxide layer in fine‐grained 316L to form a continuous protective scale. These findings provide a critical foundation for optimizing microstructural characteristics under LBE conditions, offering a basis for selecting materials that achieve the optimal balance between corrosion resistance and mechanical integrity in fourth‐generation lead‐cooled reactor containment systems. This work provides actionable recommendations for selecting structural materials for use in heavy liquid metal applications.