Tensile properties of 9Cr-1MoVNb and 12Cr-1MoVW steels irradiated to 23 dpa at 390 to 550deg C

Normalized-and-tempered 9Cr-1MoVNb and 12Cr-1MoVW steels were irradiated in the Experimental Breeder Reactor II (EBR-II) at 390, 450, 500, and 550deg C to displacement damage levels of up to 23 to 25 dpa. Tensile tests were conducted at the irradiation temperatures on three types of specimens: irradiated specimens, normalized-and-tempered specimens, and specimens thermally aged 5000 h at the irradiation temperatures. Observations from these tests were compared with results on these same materials irradiated in EBR-II at the same temperatures to 9 to 13 dpa. Irradiation of specimens at 390deg C to 23 to 25 dpa caused an increase in strength and a decrease in ductility relative to the aged and unaged control specimens; however, there was little change from the specimens irradiated to 9 to 13 dpa. After irradiation at 450, 500, and 550deg C, there was little difference between the irradiated specimens, the normalized-and-tempered specimens, and the specimens aged for 5000 h. Results were interpreted in terms of the precipitate and dislocation microstructures developed during normalizing and tempering, thermal aging, and irradiation. (orig.)