マルテンサイト系ステンレス鋼の応力腐食割れおよび腐食疲労き裂進展特性の評価

摘要

マルテンサイト系ステンレス鋼は高強度，高耐食性rnといった特徴から原子力発電所や一般産業機器で用いrnられているが，塩化物，高温高圧環境等の苛酷な使用rn環境下で応力腐食割れ（Stress Corrosion Cracking，SCC）rnおよび腐食疲労（Corrosion Fatigue，CF）が問題となっrnている．%This work aimed to characterize crack growth of stress corrosion cracking (SCO and corrosion fatigue (CF) for two types of martensitic stainless steel, SUS410 and SUS410S, in air and hydrogen charging environment. The crack growth characteristics were evaluated by fracture mechanics tests which were conducted under stress intensity factor, K-control, and by acoustic emission (AE) monitoring. Crack growth acceleration was observed in the hydrogen charging environment. The SCC characteristics of SUS410S were slower than those of SUS410, while the CF characteristics of both materials were similar. The observations of the fracture surface suggested that the hydrogen embrittlement cracking occurred near the surface of the specimen, where hydrogen diffused more quickly. Based on the AE and electrochemical analyses, the difference in SCC characteristics of both materials was attributed to the penetration of the hydrogen through the passive film for each material. Since the crack growth characteristics of the both materials exhibit the same relation, the passive film is broken by cyclic loading in CF tests.