Influence Of Nitrogen On Radiation Resistance Of Austenitic Stainless Steel

Nitriding austenitic stainless steel were widely used as structure material on nuclear reactors because of their good mechanical properties and their superior corrosion and radiation resistance over a wide range of temperature and pressure. However, it was well known that the solution annealed austenitic stainless steels such as 316L(N) are not suitable for high dose applications (in DEMO> 70 dpa) due to their irradiation swelling. Previous studies have shown that the radiation resistance of austenitic stainless steel was increasing with the nitrogen content while the mechanism was unclear. It has been shown experimentally that nitrogen interacts strongly with vacancy, and radiation swelling was the macro performance of the vacancies evolution. Thus, nitrogen might change the evolution of vacancies and restrain the radiation swelling by nitrogen-vacancy interaction. The study of interaction of nitrogen and vacancy and clusters evolution was conducive to understanding the irradiation resistance mechanism of nitrided austenitic stainless steel.The structure, characteristic and evolution of nitrogen-vacancy clusters was investigated in a face-centered-cubic (fcc) pure-Fe model of first-principle calculations based on density function theory. It was domenstrated that N was most stable in the [100]/[010] first nearest-neighbor octahedral interstice sit around vacancy. A vacancy can stably bind up to two dumbbell-N atoms with [100]/[010] orientation. Nitrogen and vacancy bound strongly and formed stable N-vacancy (VnNm) clusters. The most stable VnNm clusters had two types with fixed banded structures and n/m ratios, one extended to [110] and the other extended to [001]. Nitrogen had dual influence on vacancies evolution. Unstable VnNm clusters with insufficient N had more growth probability because N decreased the binding energy of vacancies. Stable VnNm clusters rejected N, vacancy and other VnNm clusters and had less growth probability by N-N repulsion and special structure. This study suggested that we can ensure sufficient nitrogen to increasing the swelling resistance of austenitic stainless steel according to radiation-induced vacancy concentration.