Tensile and stress corrosion cracking behavior of ferritic-martensitic steels in supercritical water

Tensile and stress corrosion cracking behavior of ferritic-martensitic steels in supercritical water were studied in order to evaluate the suitability of these steels for supercritical water nuclear reactor concept. The ferritic-martensitic steels tested in this study consisted of T91, HCM12A, HT-9, weld T91, and weld HCM12A. A series of constant extension rate tensile (CERT) tests at a strain rate of 3 × 10−7 s−1 were conducted in supercritical water over a temperature range of 400-600 °C and pressure 24.8 ± 0.07 MPa. CERT tests in argon and in supercritical water with 100 and 300 appb dissolved oxygen also were performed at 500 °C to compare the effect of environment. The results show that HT-9 exhibited the highest yield and maximum stresses, followed by HCM12A, and T91. The reduction in area of T91 is the highest, followed by HCM12A, and HT-9. Temperature has a great effect on tensile behavior of these steels. An increase in test temperature from 400 to 600 °C reduces the yield stress by ∼50%. Both T91 and HCM12A weld steels exhibited a slightly lower yield and maximum stresses than the base steels. Increased dissolved oxygen in the water resulted in a significant reduction of ductility. Fractography showed that all of the specimens exhibited ductile rupture except for HT-9 that showed evidence of intergranular cracking. Intergranular cracking in HT-9 is affected by temperature and oxygen concentration in supercritical water.