[en] The effect of radiation on microstructural evolution and phase transformation in Fe-50Cr-5W and Fe-50Cr-8W model alloys was examined. The 300 keV Fe⁺ ion irradiation was performed at temperatures of 550, 600, 670, and 700degC at a rate of 1.4 x 10¹⁸ ions/m² s for (1.2-1.8) x 10³ s in a transmission electron microscope (TEM). The damage peak level corresponded to about 190-285 dpa. The peak depth positions of damage and Fe⁺ ion were about 60 and 100 nm, respectively. Dislocation loops were observed in the Fe-50Cr-W alloys up to 700degC. A Laves phase of tens of nanometers in size was formed in the Fe-50Cr-W alloys within a few minutes, but the formation of Laves phase decreased with increasing irradiation temperature. Sigma-phase grains of about 50-100 nm in size and micro-crystallines were observed in the alloys irradiated at 670 and 700degC. However, in the specimen aged at 700degC for 1000 h and the one aged at 700degC for 10 h after 80% CW, only the Laves phase had formed and no sigma phase was observed in the Fe-50Cr-W alloys. These results indicate that Fe⁺ ion irradiation can strongly influence the Laves and sigma phase transformations, and microstructural development, in the Fe-50Cr-W alloys. (author)