Fe-C-Cu, Fe-C-Ni, and Fe-C-Cu-Ni model alloys were prepared in order to investigate the effects of copper and nickel on radiation embrittlement. They were irradiated with 4 MeV Ni³⁺ ions at 563 K to introduce displacement damage, followed by a micro-Vickers hardness test employing low load (0.5 g). It was observed that greater hardening occurred for samples of larger copper content, and that hardening of the samples containing both copper and nickel was greater than hardening of the ones containing copper or nickel solely for samples irradiated to 10^-2 and 10^-1 dpa. Increased hardness after annealing occurred for Fe-0.1C-0.2Cu and Fe-0.lC-0.4Cu. Small defect clusters of approximately 3 nm in diameter were observed by transmission electron microscopy (TEM) of the irradiated Fe-0.1C and Fe-0.1C-0.4Cu samples, which cause hardening.