Corrosion and corrosion fatigue behaviors of 9cr steel in a supercritical water condition

By using coupons and compact tension (CT) samples, the corrosion and corrosion fatigue behaviors of modified 9Cr–MoVNb steel, T91, in a deaerated supercritical water (SCW) condition were investigated. Water pressure was 25 MPa and the test temperatures were 370 and 500 °C. Before and after the 200 h exposure tests, the weight of the samples was measured. The weight of the coupons exposed to 500 °C water increased while that in 370 °C water decreased. The samples exposed to both these conditions were analyzed by using SEM-EDX, AES, and XRD. The analyses showed that only an oxidation (oxide formation) on the sample in the SCW condition occurred while an anodic dissolution in the subcritical condition was dominant. Fatigue crack growth rates (FCGR) determined in the water conditions were compared with those in air. The FCGRs of the alloy were higher in the supercritical and subcritical aqueous conditions than those in air. From the standpoint of a corrosion or an oxidation, the corrosion fatigue behavior of the steel in a supercritical environment was discussed.