FRACTURE BEHAVIOR OF OXIDIZED GRAIN BOUNDARY IN NEUTRON-IRRADIATED STAINLESS STEEL

摘要

Effects of oxidation on cohesive strength of a grainboundary (GB) was investigated by micro-tensile testingfor stainless steel specimen neutron-irradiated to 73 dpaand then immersed in simulated PWR primary water at320°C. The micro-specimens were fabricated with anoxidized GB and a non-oxidized GB (as-irradiated). Thespecimen with the oxidized GB failed at 1100 Mpa,whereas the specimen with the non-oxidized GB failed at2600 Mpa. It was found that GB oxidation woulddecreased the cohesive strength to one third that of theas-irradiated GB. By considering the stress concentrationon GBs due to deformation constraint in a polycrystallinematerial and dislocation channeling deformation, it wassuggested that the oxidized GBs would crack when thetensile stress was applied on the neutron-irradiatedstainless steel used in high temperature water at the samelevel as the initiation threshold stress of the irradiationassistedstress corrosion cracking (IASCC). Intergranularcracking propagation by repetition of further GBoxidation and its fracture was thought to be one of theinitiation mechanisms of IASCC.