Evaluation of the Effects of Thermal Aging of Austenitic Stainless Steel Welds Using Small Punch Test

Abstract

Austenitic stainless steels and associated welds have been widely used for the pressurizer surgeline of the pressurized water reactors (PWRs). Though the amount of the ferrites in the welds is generally low, the relatively high operating temperature of surgeline may cause the degradation of fracture resistance due to thermal aging during the long-term operation. In this study, the mechanical property changes caused by the thermal aging were evaluated for the ER316L and ER347 welds as well as CF8 M. The materials were thermally aged at 400 °C for 5,000 h and the properties were measured at room temperature and 320 °C. The fracture resistance was measured using 1/2T-CT specimen by normalization method. In addition, small punch (SP) test was performed at both temperatures and the results were used to estimate the tensile property and fracture resistance of the stainless steel welds and CF8 M. Based on the results, correlations were developed to estimate the fracture resistance using the load-displacement curve of SP tests. Also, the fracture surfaces of CT and SP test specimens were compared and discussed in view of the effect of thermal aging on microstructure.