INSTRUMENTED IMPACT PROPERTIES OF SOME ADVANCED NUCLEAR-REACTOR PRESSURE-VESSEL STEELS

Steels used to construct nuclear reactor pressure vessels are low-allo y ferritic steels. These steels should have good impact properties, i. e., low transition temperature and high upper shelf energy, both befor e and during service conditions. The most important service condition is the neutron irradiation. Extensive research and development was con ducted to develop such steels. Instrumented impact testing was conduct ed on three advanced pressure vessel steels and, for comparison, a con ventional pressure vessel steel, Both microstructures and fracture sur faces were examined using optical and scanning electron microscopic (S EM) techniques. In general, the advanced steels showed much better imp act properties (lower ductile-brittle transition temperature and highe r upper shelf energy) than the conventional steel. Load-time traces sh owed that increase in the fracture energy was mainly due to increase i n the fracture propagation energy rattler than the initiation energy. Improvement in the toughness level of the advanced steels compared to that of the HSST steel was related to the difference in chemical compo sition, microstructure, and fracture surface morphology.