RAFM steel — reduced-activation ferritic-martensitic steel — is the leading candidate structural material for fusion blankets: a chromium steel whose alloying elements are chosen so that neutron bombardment leaves only short-lived radioactivity.
RAFM steel is the flagship of the 📝low-activation materials family, and its design logic is substitution: start from the proven 9-percent-chromium heat-resistant steels of conventional power engineering, then replace the elements that activate badly with metallurgical stand-ins that do the same mechanical job — molybdenum gives way to tungsten, niobium to tantalum. The result keeps the creep strength and weldability of its commercial ancestors while shedding their long-lived activation products. The best-characterized reference grades are Europe's Eurofer97 and Japan's F82H, backed by decades of irradiation data.
The ferritic-martensitic part of the name is as load-bearing as the reduced-activation part. The body-centered-cubic crystal structure of these steels resists the void swelling that plagues conventional austenitic stainless steels under heavy 📝neutron damage, which is what qualifies them for the blanket — the component that absorbs the plant's neutrons, converts their energy to heat, and breeds 📝tritium from lithium. Their working temperature window, roughly 350 to 550 degrees Celsius, is bounded below by irradiation embrittlement and above by loss of creep strength, and widening that window — through oxide-dispersion-strengthened variants and related development lines — is an active frontier of fusion materials research.