EFFECTS OF NEUTRON-IRRADIATION ON MICROSTRUCTURAL EVOLUTION IN CANDIDATE LOW-ACTIVATION FERRITIC STEELS

Fe-(2.25-12)Cr-2W-V, Ta low activation ferritic steels (JLF series ste els) were developed in the fusion materials development program of Jap anese universities. Microstructural observations, including precipitat ion response, were performed after neutron irradiation in the FFTF/MOT A. The preirradiation microstructure was stable after irradiation at l ow temperature (< 683 K). Recovery of martensitic lath structure and c oarsening of precipitates took place above 733 K. Precipitates observe d after irradiation were the same as those in unirradiated materials i n 7-9Cr steels, and no irradiation induced phase was identified. The i rradiation induced shift in DBTT in the 9Cr-2W steel proved to be very small which is a reflection of stable precipitation response in these steels. A high density of fine alpha' precipitates was observed in th e 12Cr steel which might be responsible for the large irradiation hard ening found in the 12Cr steel. Void formation was observed in 7-9Cr st eels irradiated at 683 K, but the amount of void swelling was very sma ll.