The mechanical properties and microstructural changes in 15Kh2MFA steel after neutron irradiation of the base metal and the weld metal have been studied. The surveillance specimens of a nuclear power plant reactor with a low copper (Cu) content (Cu < 0.08 wt% for the base metal, Cu < 0.06 wt% for the weld metal) were used for the investigation. The characteristic radiation-induced defects were found by transmission electron microscopy (TEM) starting from a neutron fluence of 4 × 10²³ n/m² (E > 1 MeV). “Black dots” concentrating to dislocation lines coexist with small resolvable dislocation loops at higher neutron fluences. Refinement of the vanadium carbide (VC) particles has been demonstrated also in the ferritic grains of the weld metal.

The mechanical properties of both the base metal and the weld metal result in a high radiation stability. The observed microstructural changes correspond to the measured values of the radiation embrittlement and strengthening, but the increase in the flow stress cannot be explained on the basis of the visible radiation damage alone.