Microstructural evolution of Y 2O 3 and MgAl 2O 4 ODS EUROFER steels during their elaboration by mechanical milling and hot isostatic pressing

Abstract

Different ODS EUROFER steels reinforced with Y 2O 3 and MgAl 2O 4 were elaborated by mechanical milling and hot isostatic pressing. Good compromise between strength and ductility could be obtained but the impact properties remain low (especially for the Y 2O 3 ODS steel). The materials were structurally characterized at each step of the elaboration. During milling, the martensite laths of the steel are transformed into nano-metric ferritic grains and the Y 2O 3 oxides dissolve (but not the MgAl 2O 4 spinels). After the HIP, all the ODS steels remain ferritic with micrometric grains, surrounded by nano-metric grains for the Y 2O 3 ODS steels. The mechanisms in the Y 2O 3 ODS steels are complex: the Y 2O 3 oxides re-precipitate as nano-Y 2O 3 particles that impede a complete austenitization during the HIP. The quenchability of the ODS steels is modified by the milling process, the oxide nature and the oxide content. Eventually, the advantages and drawbacks of each oxide type are discussed.