Evaluation of ferritic alloy Fe-2-1/4Cr-1Mo after neutron irradiation - microstructure development

Microstructural examinations are reported for nine specimen conditions of 2-1/4Cr-1Mo steel which had been irradiated by fast neutrons over the temperature range 390 to 5100C. Two heats of material were involved, each with a different preirradiation heat treatment, one irradiated to a peak fluence of 5.1 x 1022 n/cm2 (E > 0.1 MeV) or 24 dpa and the other to 2.4 x 1023 n/cm2 (E > 0.1 MeV) or 116 dpa. Void swelling is found following irradiation at 4000C in both conditions and to 4800C in the higher fluence conditions. Concurrently dislocation structure and precipitation formed. Peak void swelling, void density, dislocation density and precipitate number density developed at the lowest temperature, approx. 4000C, whereas mean void size, and mean precipitate size increased with increasing irradiation temperature. The examination results are used to provide interpretation of in-reactor creep, density change and post irradiation tensile behavior