Effect of Ce on creep damage behaviors of 316LN austenitic stainless steel at 650 °C/225 MPa

The influence of trace Ce addition on the creep damage behavior of 316LN austenitic stainless steel (316LN) under 650 °C/225 MPa was investigated through microstructural characterization and first-principles calculations, and the underlying mechanism was elucidated. The results show that the addition of 0.011 wt% Ce extends the creep rupture life of 316LN steel from 175h to 253h but significantly reduces the creep rupture strain from 62 % to 25 % and shifts the fracture mode from trans -granular to intergranular failure. The formation of intergranular cracks is closely related to the nucleation and growth behavior of cavities in the vicinity of dispersed Cr-containing M 23 C 6 carbides. First-principles calculations reveal that the solute Ce atoms distribute along grain boundaries (GBs) independently of Cr-rich carbides, inhibiting GB migration and enhancing creep resistance. However, Ce segregation reduces the cohesive strength of GBs, making transverse GB regions with Ce segregation more susceptible to decohesion under high stress, leading to cavity nucleation. Continuous cavity nucleation weakens GB tensile strength, while interfacial cracking of the chromium carbides promotes cavity coalescence, forming intergranular microcracks. The propagation of these microcracks ultimately induces intergranular fracture and reduces creep plasticity.