In order to evaluate the SCC susceptibility of cast austenitic stainless steels which are often used for the main coolant piping of pressurized water reactors (PWRs), the slow strain rate test (SSRT) and the constant load test (CLT) of materials were performed in simulated primary water at
360°C. The cast austenitic stainless steels contain ferrite phase ranging from 8 to 23 % and its mechanical properties are affected by long time thermal aging. Therefore, the influence of the ferrite content and thermal aging on the SCC susceptibility of this stainless steel was evaluated with
three materials ranging ferrite contents of 23%, 15% and 8%. The reduction in area observed by the SSRT in simulated primary water at 360°C was smaller than that obtained by the tensile test in air at the same temperature. The SCC susceptibility was evaluated by reduction ratio defined by the ratio of the reduction in area by the SSRT to that by the
tensile test. The reduction ratio was not clear for low ferrite specimens, but apparently decreased with increasing aging time for the specimen with 23% ferrite. This change by aging time can be explained as follows: (1) the brittle fracture in the unaged specimens is mainly caused by
quasi-cleavage fracture in austenite phase. (2) After aging, it becomes a mixture of quasi-cleavage fracture in both austenite and ferrite phases and phase boundary fracture of both phases.
Keywords: Cast austenitic stainless steel, Thermal aging, Slow Strain Rate Test (SSRT), Constant Load Test (CLT), Primary Water Stress Corrosion Cracking (PWSCC)