Abstract
Constant extention rate testing on sensitized type 304 stainless steel was carried out in high temperature purified water with and without 60Co γ-ray irradiation to demonstrate the effect of the environmental condition on the sensitivity to intergranular stress corrosion cracking (IGSCC). The cracking behavior was considerably influenced by a simultaneous exposure to high dissolved exygen (DO) and temperature, whereas γ-ray exposure exhibited rather a minor contribution to it. IGSCC occurrence was found under DO concentration more than 500ppb and at temperature higher than 200°C. Under the other environmental condition, the tensile specimen was failed via either transgranular stress corrosion cracking (TGSCC) or ductile failure mode.
γ-ray exposure, however, played an interesting role depending on the DO concentration. It forms rather a protective environment at below 500ppb DO and an aggressive one at over several ppm DO.
It is considered that the result is determined through the basic mechanism as follows: (1) an enhanced cathodic reaction by oxidative species formed by radiolysis, which becomes more dominant under a higher DO concentration; (2) an oxidation reaction of metallic cations dissolved in the vicinity of crevice tips, which causes plugging of the crevice.
