Creep–Fatigue–Oxidation Behaviors of 316H in Oxygen‐Saturated Lead‐Bismuth Eutectic

Austenitic stainless steel 316H is a candidate structural material for lead‐bismuth‐cooled fast reactors (LFRs). Understanding its creep–fatigue–oxidation (CFO) behavior in liquid lead‐bismuth eutectic (LBE) is therefore essential for assessing structural reliability. This study systematically investigates CFO behavior of 316H stainless steel in oxygen‐saturated LBE at 550°C–600°C, with an emphasis on the coupled influence of environmental exposure and holding time during cyclic loading. The results demonstrate a distinct, time‐controlled transition in damage mechanisms. Short holding times promote oxidation‐assisted transgranular cracking, driven by repeated rupture of a discontinuous oxide film and rapid ingress of LBE, leading to a 5–10‐fold reduction in fatigue life compared with air. At intermediate holding durations, enhanced grain‐boundary oxidation and stress‐assisted diffusion cause mixed transgranular–intergranular cracking. Under long holding time, a dense duplex oxide develops and remains stable within the crack cavity, producing crack‐tip blunting, suppressing LBE penetration, and shifting the dominant mechanism toward creep‐assisted intergranular fracture. Microstructural, compositional, and kinetic analyses collectively demonstrate that oxide‐film evolution, grain‐boundary degradation, and time‐dependent relaxation act in concert to regulate CFO behavior. These mechanistic findings delineate the time‐dependent pathways of environmental degradation in oxygen‐saturated LBE and form a scientific basis for evaluating material performance and guiding structural design for LFR applications.