Engineering the Next Generation of Industrially Scalable Fusion-Grade Steels

Abstract

Future fusion power plants require structural materials that can withstand extreme operating conditions, including high coolant outlet temperatures, mechanical loading, and radiation damage. Reduced-activation ferritic martensitic (RAFM) steels are a primary candidate as a structural material for such applications. This study demonstrates the successful production of a 5.5-tonne RAFM billet via electric arc furnace (EAF) technology, enabling scalable, cost-effective manufacturing. The resulting UK-RAFM alloy offers superior tensile strength and creep lifetime performance compared to Eurofer97. This is attributed to alterations in the initial forging process during manufacture. Modified thermomechanical treatments (TMTs) were subsequently applied to the UK-RAFM, which are shown to enhance the tensile strength further, particularly at 650 °C. Building on this, an Advanced RAFM (ARAFM) steel was designed to exploit the benefits of optimised chemistry to encourage metal carbonitride (MX) precipitate evolution alongside bespoke TMTs. Challenges around ensuring suitable processing windows in these steels, to avoid the over-coarsening of MX precipitates or the formation of deleterious delta-ferrite, are discussed. A subsequent 5.5-tonne ARAFM billet has since been produced using EAF facilities, with performance to be reported separately. This work highlights the synergy between alloy design, process optimisation, and industrial scalability, paving the way for a new generation of low-cost, high-volume, fusion-grade steels.