Effect of Oxidation Chemistry of Supercritical Water on Stress Corrosion Cracking of Austenitic Steels

Austenitic steel is a candidate material for supercritical water-cooled reactor (SCWR). This study is to investigate the stress corrosion cracking (SCC) behavior of HR3C under the effect of supercritical water chemistry. A transition phenomenon of the water parameters was monitored during a pseudocritical region by water quality experiments at 650 degrees C and 30 MPa. The stress-strain curves and fracture time of HR3C were obtained by slow strain rate tensile (SSRT) tests in the supercritical water at 620 degrees C and 25 MPa. The concentration of the dissolved oxygen (DO) was 200-1000 mu g/kg, and the strain rate was 7.5 x 10(-7)/s. The recent results showed that the failure mode was dominated by intergranular brittle fracture. The relations of the oxygen concentration and the fracture time were nonlinear. 200-500 mu g/kg of oxygen accelerated the cracking, but a longer fracture time was measured when the oxygen concentration was increased to 1000 mu g/kg. Chromium depletion occurred in the oxide layer at the tip of cracks. Grain size increased and chain-precipitated phases were observed in the fractured specimens. These characteristics were considered to contribute to the intergranular SCC.