Icone23-1158 effect of oxidation chemistry of scw on stress corrosion cracking of austenitic steels

Austenitic steel is a candidate material for Supercritical Water-Cooled Reactor. This study is to investigate stress corrosion cracking behavior of HR3C under effect of supercritical water chemistry. A transition phenomenon of water parameters was monitored during a pseudo critical region by water quality experiments at 650 °C and 30 MPa.The stress-strain curves and fracture time of HR3C were obtained by slow strain rate tensile tests in supercritical water at 620 °C and 25 MPa. The concentration of dissolved oxygen was 200-1000 μg/kg and the strain rate was 7.5×10^/s. Recent results showed the failure mode was dominated by intergranular brittle fracture. The relations of oxygen concentration and fracture time were nonlinear. 200-500 μg/kg of oxygen accelerated the cracking but a longer fracture time was measured when oxygen concentration was increased to 1000 μg/kg. Chromium depletion occurred in the oxide layer at the tip of cracks. Grain size increased and chain precipitated phases was observed in the fractured specimens. These characteristics were considered to be contributive to the intergranular stress corrosion cracking.