Model alloys of ferritic steels were irradiated to a low fluence of 1 × 10²³ neutrons (n)/m² at temperatures 544, 580, and 599 K. These alloys were pure iron, Fe-0.1C, Fe-0.1C-0.15Cu, and Fe-0.1C-0.28Cu. Specific attention was given to the copper-containing alloys in correlating microstructural changes as observed in the transmission electron microscope (TEM) with hardness changes measured using Vickers microhardness tests. The post-irradiation microstructure did not exhibit characteristic radiation damage; no voids, bubbles, or dislocation loops were observed. The hardness changes were related to the semi-quantitatively obtained amount of copper not bound in TEM-observable copper-containing precipitates. The copper unaccounted for in observed precipitates was shown to be the primary influence on hardness changes.