Post-irradiation annealing effects on hardness and IASCC susceptibility in stainless steels

The effects of post-irradiation annealing on hardness and grain boundary corrosion related to stress corrosion were investigated on type 304 and 304L stainless steels irradiated to 5.3 x 1024 n/m2 (E>1 MeV). Hardness tests, 10% oxalic acid tests and double loop electrochemical potentiokinetic reactivation (EPR) tests were conducted after annealing at 400 to 1000 degrees C for one hour. Radiation anneal hardening was observed at 500 degrees C and was more pronounced on alloys containing a higher amount of C and Si. The hardness recovered by annealing at 600 degrees C and above. In the oxalic acid tests, the irradiated type 304 stainless steel was sensitized as well as the unirradiated specimen, and grain boundary attack in the former was slightly pronounced than in the latter. In the EPR test, the surface morphology and the annealing temperature dependence of the reactivation ratio in the irradiated specimens were different from those in the unirradiated specimens. These differences indicated that changes in Cr carbide an Cr depletion near the grain boundary during annealing would be influenced by a pre-existing irradiation induced microstructure and grain boundary segregation. Annealing at 1000 degrees C resulted in a full recovery of hardness, grain boundary corrosion and IGSCC susceptibility determined by a slow rate (SSR) test in high temperature water