Influence of Y2O3 and Fe2Y additions on the formation of nano-scale oxide particles and the mechanical properties of an ODS RAF steel

The main goal of this work was to manufacture an oxide dispersion strengthened (ODS) reduced activation ferritic steel from a pre-alloyed, gas atomised Fe–14Cr–2W–0.2Ti (in wt.%) powder mechanically alloyed with either 0.3%Y2O3 or 0.5%Fe2Y particles and consolidated by hot isostatic pressing, and to investigate its microstructure, microhardness and Charpy impact properties. r oxygen content was measured in the ODS Fe2Y steel than in the ODS Y2O3 steel. However, the mean size of nanoclusters in the ODS Fe2Y steel was found larger, whereas density was smaller, than in the ODS Y2O3 steel. In addition, the nanoclusters in the ODS Fe2Y steel appear less stable upon thermal annealing at 1350 °C for 1 h. Vickers microhardness measurements revealed that after HIPping the ODS Y2O3 is about 40% harder (366 HV0.1) than the ODS Fe2Y (260 HV0.1). After heat treatment at 1350 °C the microhardness of both alloys was found smaller by about 30%. The ODS Fe2Y steel was found to exhibit a much better Charpy impact behaviour, with an upper shelf energy of 8.8 J and a ductile-to-brittle transition temperature of −24 °C. The differences in mechanical properties were discussed in terms of the oxygen content as well as in the mean size, number density and crystallographic structure of the nanoclusters.