소형펀치 파단에너지 천이곡선을 활용한 원자로용기강의 천이온도 평가

Abstract

The small punch (SP) test is one of the small specimen test techniques, and standardization of the SP test method for evaluating the mechanical properties of metallic materials is in progress. In this study, the impact transition temperature of reactor pressure vessel steels (RPV) in nuclear power plants was estimated using the draft standard SP test method. The SP fracture energy (E-SP) and normalized SP fracture energy (E-NSP) of the RPV steels were evaluated at various temperatures, and their transition curves were derived and compared to the transition curve in the Charpy V notch (CVN) test. The SP transition region appeared at a much lower temperature range than that of the CVN owing to the size and notch effect. Ductile brittle transition temperature (DBTT) in the SP transition curve showed a linear relationship with DBTT and T-41J in the CVN transition curve. The ductile to brittle transition behaviors of SP specimens were analyzed using fractographs and compared with the transition curves in E-SP and E-NSP. E-NSP started to decrease at the temperature at which the SP ductile to brittle transition behavior occurred, and this means that the E-NSP transition curves were in good agreement with transition behavior in the SP test. However, the E-SP transition curves did not match transition behavior Using DBTT in the E-NSP transition curve is appropriate to estimate the CVNDBTT and T-41J.