In-situ SCC observation of thermally-sensitized and cold-worked type 304 stainless steel irradiated to a neutron fluence of 1 × 1025 n/m2

Crack initiation and crack growth processes of irradiation assisted stress corrosion cracking of stainless steels were studied by slow strain rate testing (SSRT) in oxygenated high temperature 561 K water. In-situ observation was carried out during SSRT for type 304 stainless steel irradiated to a neutron fluence of 1.0 × 1025 n/m2 (E > 1 MeV) at 323 K in the Japan material testing reactor. The specimens were subjected to solution annealing, thermal sensitization, or cold working prior to neutron irradiation. The solution annealed material exhibited a combination of transgranular stress corrosion cracking (TGSCC) and ductile fracture, and almost all intergranular stress corrosion crackings were observed in the thermally-sensitized material. In the cold-worked material, cracking was introduced before the maximum stress was reached, and the fracture mode changed from TGSCC to ductile fracture to transgranular cracking together with the progress of crack growth in one direction.