Separation of microstructural and microchemical effects in irradiation assisted stress corrosion cracking using post-irradiation annealing

Post-irradiation annealing (PIA) was conducted in order to clarify the role of microstructural and microchemical effects on irradiation assisted stress corrosion cracking (IASCC) susceptibility in simulated pressurized water reactor (PWR) primary water. Microstructures, hardening, radiation-induced segregation and IASCC susceptibility were examined in cold-worked SUS 316 stainless steels irradiated to 25 dpa in a PWR after annealing at 673-823 K for 1 h. IASCC susceptibility, microstructures and hardening recovered as the annealing temperature increased whereas the grain boundary segregation of Cr and Ni remained almost unchanged. The results suggested that the change in IASCC susceptibility due to annealing is not attributed to the change in grain boundary segregation but to the change in microstructures and hardening. The fact that a smaller recovery of radiation hardening caused a larger IASCC susceptibility suggested that a threshold hardening level exists for the occurrence of IASCC.