Alloy Designing Study for Improving Mechanical Properties of SA 508 Steel for Nuclear Reactor Pressure Vessel

摘要

This study is concerned with the development oflow-alloy steels for nuclear reactor pressure vessel byinvestigating the effects of alloying elements on mechanicalproperties of base metals and heat affected zones (HAZ's).Four kinds of steels with different alloying elements werefabricated by vacuum-induction melting and heat treatment,and their tensile properties and Charpy impact toughness wereevaluated. Microstructural analyses indicated that coarseM_3C-type carbides and fine M_2C-type carbides wereprecipitated along lath boundaries and inside laths, respectively.In the steels having lower carbon content and highermolybdenum content, the amount of fine M_2C carbidesgreatly increased, while that of coarse M_3C carbidesdecreased, thereby leading to the improvement of tensileproperties and impact toughness. Their simulated HAZ's alsohad sufficient impact toughness after post-weld heat treatment.These findings suggested that low-alloy steels with highstrength and toughness could be processed by reducing theamount of carbon and manganese and by raising the amount of molybdenum.