The behavior of low C9Cr2Mo steel in a fast breeder reactor irradiation environment

Abstract Low carbon-9Cr-2Mo steel has been irradiated in EBR-II with the fluence up to 3×10 26 n/m 2 at temperatures of 673 723, 823 and 923 K. Post irradiation examination was carried out in terms of tensile properties, fracture modes and microstructural change by means of transmission electron microscopy. Radiation hardening was observed below 773~823 K irradiation temperature, while at higher irradiation temperatures little difference was observed in the tensile strength between unirradiated and irradiated material. Fractography revealed the ductile dimple-type failures without any sign of cleavage or grain boundary fracture. Transmission electron microscopic observation indicated that the steel consisted of duplex microstructure with tempered martensite and δ-ferrite. Martensite remained stable up to 823 K and underwent, at higher temperatures, recovery and recrystallization. In the ferrite grains, irradiation-related microstructural changes were not clear, however at 823 K. a significant precipitation took place. No voids were observed in either structure.