IMPACT BEHAVIOR OF REDUCED-ACTIVATION FERRITIC STEELS IRRADIATED IN THE FAST FLUX TEST FACILITY

Reduced-activation Cr-W steels with chromium concentrations varying from 2.25 to 12 wt% were irradiated at 365-degrees-C to approximately 7 dpa in the Fast Flux Test Facility. Irradiation caused a loss of toughness for all steels, as measured in Charpy impact tests; increases in the ductile-brittle transition temperature (DBTT) and decreases in the upper-shelf energy were observed after irradiation. Two steels with 9% Cr showed the greatest resistance to the effects of irradiation: the DBTT of a 9% Cr steel with 2% W and 0.25% V increased by 68-degrees-C during irradiation; this same composition with an addition of 0.07% Ta developed an increase in DBTT of only 4-degrees-C. These shifts in DBTT compared to increases of over 100-degrees-C for the rest of the steels. Observations on the steels with 2.25% Cr indicated that a steel containing a combination of 2% W and 0.25% V was less severely affected by irradiation than steels with vanadium and no tungsten, tungsten and no vanadium, or with 1% W and 0.25% V.