Ferritic/martensitic dual-phase steel as fusion reactor materials

In ferritic/martensitic steels, the swelling rate is much lower than in austenitic steels. Therefore, ferritic/martensitic steels may become the next candidate alloys for the first wall of future fusion reactors. Until now, the martensitic steels HT-9 and modified 9Cr-1Mo steel have been investigated. These steels have excellent high-temperature creep properties but are not necessarily better in Ductile Brittle Transition Temperature (DBTT) properties than austenitic steel. Especially their weldability is a problem. For these reasons new ferritic/martensitic dual-phase steels have been considered. In this presentation, the advantages and disadvantages in their use as fusion reactor materials will be discussed. The recommended compositions are mainly low-C 9Cr-1 or 2Mo including some modifications. Since these alloys have wider two-phase regions than 9Cr-1Mo steel, after normalizing, a ferritic/martensitic structure with a fixed percentage of ferrite can be obtained. The mechanical properties, weldability and other properties are compared between single- and dual-phase steels. And the characteristics of the ferritic/martensitic dual phase steels are introduced. (orig.)