SCC behavior of austenitic and martensitic steels in supercritical pressurized water

Stress corrosion cracking behavior of austenitic (type 316L) and martensitic (JLF-1LN) steels has been investigated in a supercritical pressurized water (SCPW) environment. Slow strain rate tensile tests were carried out at 673 and 783 K at strain rates 6.4 × 10−4 s−1 and 5 × 10−7 s−1 in SCPW of 25 MPa pressure and 8 ppm dissolved oxygen. Austenitic steel showed a strong strain rate dependence of the total elongation at 783 K, while no difference was observed at 673 K. At low strain rate, the elongation was reduced at 673 K and was accompanied by transgranular stress corrosion cracking. Martensitic steel showed a strong temperature dependence of tensile strength. This is due to the dislocation-rate controlling mechanism or thermally activated mechanism. Scanning electron microscope observations revealed that JLF-1LN steels showed a brittle fracture mode in the limited area close to the specimen surface, while in the case of austenitic steel, transgranular stress corrosion cracking occurred for almost whole specimen cross section.