Development of castable nanostructured alloys as a new generation RAFM steels

Castable nanostructured alloys (CNAs) are being developed as a new generation of reduced-activation ferritic-martensitic (RAFM) steels to overcome certain limitations of the current RAFM steels, such as their narrow operating temperature range and associated low strength at high temperatures. Six CNAs were developed and examined, exhibiting noticeably increased yield strength, tensile strength and creep resistance as compared to the current RAFM steels, which are comparable to ODS-Eurofer (0.3% Y₂O₃) at 650 °C. The enhanced strength of CNAs is also associated with a beneficial increase in Charpy impact upper-shelf energies, up to ∼2.5 times that of the current RAFM steels, with comparable ductile-brittle transition temperatures. A broad analysis of microstructure, alloy chemistry and grain size analyses clearly support the mechanisms that explain the mechanical property improvements of these CNAs, providing essential insight for further development of advanced RAFM steels to meet the challenges of future fusion reactors.