SA508 Gr.1A 저합금강의 기계적특성에 영향을 미치는 이상영역열처리 및 Pre-tempering 열처리의 영향 = Effect of Intercritical Heat Treatment and Pre-tempering on Mechanical Properties of SA508 Gr.1A Low Alloy Steels

다국어 초록 (Multilingual Abstract)

To apply the leak-before-break (LBB) concept to the main steam line piping of nuclear power plants,the use of SA508 Gr.1A low-alloy steel is being considered. To increase the LBB safety margin, it is essentialto improve the strength and toughness of the material. In this study, intercritical heat treatment (IHT) andpre-tempering were applied to V-added SA508 Gr.1A low-alloy steel, and the effects of heat treatments onmechanical properties and LBB safety margin were analyzed. IHT resulted in the formation of fine grainsat the grain boundaries and the decomposition of coarse cementite, which led to an improvement in impacttransition toughness and J-R fracture resistance without a significant decrease in strength. The applicationof pre-tempering promoted the formation of nano-sized precipitates. It increased the strength byapproximately 30 MPa or more at room temperature and 286°C, while no significant difference was observedin impact transition toughness and J-R fracture resistance. Both heat treatments increased the LBB safetymargin from 1.37 to 1.41 by enhancing yield strength or J-R fracture resistance. However, when IHT and pretemperingwere applied together, J-R fracture resistance increased but yield strength decreased. As a result,there was no increase in the LBB safety margin.