Influence of Y 2O 3 and Fe 2Y additions on the formation of nano-scale oxide particles and the mechanical properties of an ODS RAF steel

Abstract

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%Y 2O 3 or 0.5%Fe 2Y particles and consolidated by hot isostatic pressing, and to investigate its microstructure, microhardness and Charpy impact properties. A lower oxygen content was measured in the ODS Fe 2Y steel than in the ODS Y 2O 3 steel. However, the mean size of nanoclusters in the ODS Fe 2Y steel was found larger, whereas density was smaller, than in the ODS Y 2O 3 steel. In addition, the nanoclusters in the ODS Fe 2Y steel appear less stable upon thermal annealing at 1350 °C for 1 h. Vickers microhardness measurements revealed that after HIPping the ODS Y 2O 3 is about 40% harder (366 HV 0.1) than the ODS Fe 2Y (260 HV 0.1). After heat treatment at 1350 °C the microhardness of both alloys was found smaller by about 30%. The ODS Fe 2Y 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.