The radiation hardening of iron and low-carbon steel was studied on the basis of transmission electron microscopy and tension test data. No visible defects were observed in the iron specimens after irradiation to 3.5×10¹⁹ n/cm², E>1 MeV, at 35 C, as well as after postirradiation annealing at 150 C. Marked microstructural changes occurred in steel irradiated to 2.5×10¹⁸ n/cm² both at 320 C and 450 C. In the former case a 5.1×10⁹ cm^-2 increase in dislocation density was found, while in the latter the presence of small dislocation loops of average diameter 200 Å and density 2.4×10¹⁴ cm^-3 was observed.

The approximative theoretical values of yield stress increment were calculated using the models for hardening by small dislocation loops and by a dislocation forest and were compared with the experimental values of the yield stress increment. A satisfactory agreement was obtained.