Ta添加改良ステンレス鋼の耐SCC性および耐すき間腐食性

抄録

　　In this paper, several modified stainless steels (SSs) with different contents of Ta (0.13–0.61%) and C (0.010–0.046%) were produced to measure the electrochemical potentiokinetic reactivation (EPR) ratio and investigate their crevice corrosion resistance, stress corrosion cracking (SCC) susceptibility and crack growth rate (CGR) in a simulated boiling water reactor (BWR) environment. As a result of the EPR tests, we found that the Ta/C ratio must be ≥ 13 to suppress sensitization by stabilization heat treatment. If the Ta/C ratio is ≥ 19, sensitization can be suppressed without stabilization heat treatment. In the crevice corrosion test under γ-ray irradiation, the maximum corrosion depth in the Ta-modified SSs was smaller than that in type 316L SS. Ta-modified SSs had better crevice corrosion resistance than 316L SS. In the creviced bent beam test, there was no SCC in any of the Ta-modified SSs, whereas cracks were found in four of seven specimens of 316L SS. The CGR test was conducted using 0.5 T-compact tension specimens. Crack growth rates of the Ta-modified SSs were lower than that of 316L SS. The crevice corrosion resistance and SCC resistance were improved by Ta addition. We assumed that Ta addition can improve the repassivation response.