Development of irradiation- and high-temperature resistant steels for fusion applications: Belgian contribution

In this work, we investigate alternative routes for the production of reduced activation ferritic-martensitic (RAFM) steels aiming to achieve specific improvements of their performance under fusion operational conditions. The latter impose at least two specific challenges: (i) low-temperature embrittlement (LTE) and (ii) high-temperature creep (HTC) deformation. In this work, we review the optimization routes attempted to alleviate the above noted challenges which are otherwise met in EUROFER97 steel. The development routes include: (i) reduction of manganese and carbon content coupled with alternation of other chemical elements and followed by quench & rolling procedures; (ii) alternation of spatial distribution and structural morphology of carbonitrides by varying carbon, vanadium and tantalum content based on thermodynamic computations and followed by thermo-mechanical treatment optimization; (iii) doping with zirconium/titanium and increase of tantalum content to improve ductility and toughness. The targeted enhanced performance is achieved without compromising strength and DBTT. The results of the baseline characterization including mechanical tests and microstructural characterization are presented. The contribution of the microstructural features constituting the ferritic martensitic steels into the tensile strength is analyzed based on existing mechanistic models and discussed to rationalize the improvements achieved.