EFFECT OF POST-IRRADIATION ANNEALING ON HARDENING, LOCALIZED DEFORMATION AND IASCC OF A PROTON-IRRADIATED 304 STAINLESS STEEL

摘要

Post-irradiation annealing (PIA) is potentially an effective mitigation strategy for IASCC of stainless steels in light water reactor environments. Literature has shown that proper PIA conditions can fully recover some of the unirradiated properties including IGSCC resistance. However, the underlying process by which mitigation occurs is not well understood. In this study, a commercial purity 304 stainless steel was irradiated to 10 dpa using 2 MeV protons at 360°C. Irradiated samples were annealed at different conditions: 500°C to 1 and 15h, 550°C to lh and 600°C for 10h. Constant extension rate tensile (CERT) tests were conducted in simulated BWR water at 288°C up to 10% plastic strain. Cracking susceptibility and dislocation channels were examined using SEM and LEXT interferometer, respectively. The results have shown that the decreasing trend in irradiation hardening with iron diffusion distance is consistent with the literature. IASCC susceptibility was significantly mitigated after PIA at 500°C for lh and fully removed after PIA at 500°C for 15h or 550°C for lh. The fraction of large dislocation channels dramatically dropped in the PIA samples that showed resistance to IASCC. The role of PIA in mitigation of IASCC is likely to be twofold. First, it decreases the overall yield stress of the material by removing part of irradiation hardening, thus decreasing the resolved normal stress at the grain boundaries. Second, it decreases the average dislocation channel height, which is probably linked to the decrease in the stress contribution from the channel-grain boundary intersection.