A dual-phase 12Cr oxide-dispersion-strengthened (ODS) alloy, with improved corrosion and oxidation resistance exhibits promising void swelling resistance and microstructural stability under Fe2+ ion irradiation to 800 dpa at 475 degrees C. Dispersoids were originally present in both ferrite and tempered martensite grains, with the latter having a wider range of dispersoid sizes. In both phases dispersoids > 10 nm in diameter are incoherent with the matrix, while smaller dispersoids are coherent. During irradiation the larger incoherent dispersoids shrank and disappeared. Beyond 60 dpa dispersoids in both phases approached a near-identical equilibrium size of similar to 2-2.5 nm, which appears to be rather independent of local displacement rate. Grain morphology was found to be stable under irradiation. Compared to other ferritic-martensitic alloys, the ion-induced swelling of this alloy is quite low, arising from swelling resistance associated with both tempered martensite and dispersoids in both phases. Swelling in tempered martensite is an order of magnitude less than in the ferrite phase. (C) 2015 Published by Elsevier B.V.