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

Abstract

Austenitic steel is a candidate material for supercritical watercooled 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 650آ°C and 30آ MPa. The stress–strain curves and fracture time of HR3C were obtained by slow strain rate tensile (SSRT) tests in the supercritical water at 620آ°C and 25آ MPa. The concentration of the dissolved oxygen (DO) was 200–1000  خ¼g/kg, and the strain rate was 7.5أ—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  خ¼g/kg of oxygen accelerated the cracking, but a longer fracture time was measured when the oxygen concentration was increased to 1000  خ¼g/kg. Chromium depletion occurred in the oxide layer at the tip of cracks. Grain size increased and chainprecipitated phases were observed in the fractured specimens. These characteristics were considered to contribute to the intergranular SCC.