Change of Microstructure and Toughness during the Long-term Aging of Various Steels for the First Wall Structural Materials of Fusion Reactors

Abstract

Various steels, such as a type 316 austenitic steel, its modified steels, ferritic heat resisting steels and high Mn-Cr austenitic steels have been proposed for their application to the first wall structural component of future fusion reactors and many investigations have been performed concentrating on the heavy irradiation effects of these materials. As a fundamental study, the present authors have investigated the change of microstructure during the long term aging and its effect on the toughness and fracture mode of these materials. Due to the formation of large amounts of coarse carbides within grains and on grain boundaries during the 8000 hours aging, toughness was much deteriorated and intergranular fracture and cleavage fracture were introduced by the impact test at room temperature in these materials.