Mechanical properties of unirradiated and irradiated reduced-activation martensitic steels with and without nickel compared to properties of commercial steels

Tensile and Charpy specimens of four normalized-and-tempered martensitic steels were irradiated to 23–33 dpa at 376–405 °C in the Experimental Breeder Reactor (EBR-II). The steels were the ORNL reduced-activation steel 9Cr–2WVTa and that containing 2% Ni (9Cr–2WVTa–2Ni), modified 9Cr–1Mo (9Cr–2WVTa), and Sandvik HT9 (12Cr–1MoVW). Two tempering conditions were used for 9Cr–2WVTa and 9Cr–2WVTa–2Ni: 1 h at 700 °C and 1 h at 750 °C. The 9Cr–1MoVNb and 12Cr–1MoVW were tempered 1 h at 760 °C. These heat treatments produced tempered-martensite microstructures for all steels except 9Cr–2WVTa–2Ni tempered at 750 °C, where a duplex structure of tempered and untempered martensite formed. Based on changes in tensile and Charpy impact properties, the results demonstrated the superiority in strength and ductility of the 9Cr–2WVTa reduced-activation steel over the commercial steels. Comparison of the mechanical properties after irradiation of 9Cr–2WVTa–2Ni and 9Cr–2WVTa steels indicated a favorable effect of nickel that could lead to development of a heat treatment for improved irradiation resistance.