Optimisation of the Chemical Composition and Manufacturing Route for ODS RAF Steels for Fusion Reactor Application

As the upper temperature for use of reduced activation ferritic/martensitic (RAFM) steels is presently limited by a drop in mechanical strength at about 550°C, Europe, Japan and the US are actively researching steels with high strength at higher operating temperatures, mainly using stable oxide dispersion. In addition, the numerous interfaces between matrix and oxide particles are expected to act as sinks for the irradiation-induced defects. Main R&D activities aim at finding a compromise between good tensile and creep strength and sufficient ductility, especially in terms of fracture toughness. Oxide Dispersion Strengthened (ODS) Reduced Activation Ferritic (RAF) steels appear as promising materials for application in fusion power reactors up to about 750°C. Six different ODS RAF steels, with the compositions of Fe-(12-14)Cr-2W-(0.1-0.3-0.5)Ti-0.3Y2O3 (in weight percent), were produced by powder metallurgy techniques, including mechanical alloying, canning and degassing of the milled powders, and compaction of the powders by hot isostatic pressing, using various devices and conditions. The materials have been characterized in terms of microstructure and mechanical properties. Results have been analysed in terms of optimal chemical composition and manufacturing conditions.