IMPACT BEHAVIOR OF 9CR-1MOVNB AND 12CR-1MOVW STEELS IRRADIATED IN HFIR

Charpy impact specimens of 9Cr-1MoVNb and 12Cr-1MoVW steels were irradiated in the High Flux Isotope Reactor (HFIR) at 300 and 400-degrees-C to displacement-damage levels as high as 42 dpa. For both steels, irradiation caused large increases in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy (USE). The increase in DBTT and the decrease in USE were greater at 400-degrees-C than at 300-degrees-C. At 400-degrees-C, irradiation to approximately 40 dpa produced shifts in DBTT of 204 and 242-degrees-C for the 9Cr-1MoVNb and 12Cr-1MoVW steels, respectively. These are the largest shifts ever observed for these steels and are attributed to the high helium concentration generated during irradiation in HFIR.