Synergistic Mechanism of Radiation Embrittlement of Austenitic Stainless Steels under Long-Term High-Temperature Irradiation

—The results of studying the mechanisms of fracture and embrittlement of the Kh18N9 and Kh18N10T austenitic steels under long-term neutron irradiation at elevated temperatures are given. The effects of the temperature and time of irradiation and the neutron radiation dose on the fracture strain and fracture mechanisms are analyzed. On the basis of the results obtained and specially performed experiments, a synergistic mechanism of embrittlement of the material under conditions of long-term high-temperature irradiation is proposed and substantiated, which is determined by the following two factors: thermal aging and helium diffusion. The thermal aging leads to the formation of various phases at grain boundaries and, hence, to a decrease in the grain boundary strength. Helium diffusion at elevated temperatures gives rise to the accumulation and growth of helium bubbles at weakened grain boundaries.