Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications

TLDR

Reduced activation ferritic/martensitic steels are the leading structural material for fusion reactors, and next‑generation high‑performance variants—developed via computational thermodynamics/TMT or powder‑metallurgy ODS approaches—promise longer lifetimes, better radiation resistance, higher efficiency, and lower costs. This review summarizes the current status of next‑generation high‑performance fusion steels and outlines the R&D challenges needed for their successful development. The study characterizes the new steels’ mechanical behavior—including temperature‑dependent yield strength, tensile elongation, high‑temperature creep, DBTT, fracture toughness, irradiation‑induced hardening, embrittlement, and void swelling with helium/hydrogen effects.

Abstract

Reduced activation ferritic/martensitic steels are currently the most technologically mature option for the structural material of proposed fusion energy reactors. Advanced next-generation higher performance steels offer the opportunity for improvements in fusion reactor operational lifetime and reliability, superior neutron radiation damage resistance, higher thermodynamic efficiency, and reduced construction costs. The two main strategies for developing improved steels for fusion energy applications are based on (1) an evolutionary pathway using computational thermodynamics modelling and modified thermomechanical treatments (TMT) to produce higher performance reduced activation ferritic/martensitic (RAFM) steels and (2) a higher risk, potentially higher payoff approach based on powder metallurgy techniques to produce very high strength oxide dispersion strengthened (ODS) steels capable of operation to very high temperatures and with potentially very high resistance to fusion neutron-induced property degradation. The current development status of these next-generation high performance steels is summarized, and research and development challenges for the successful development of these materials are outlined. Material properties including temperature-dependent uniaxial yield strengths, tensile elongations, high-temperature thermal creep, Charpy impact ductile to brittle transient temperature (DBTT) and fracture toughness behaviour, and neutron irradiation-induced low-temperature hardening and embrittlement and intermediate-temperature volumetric void swelling (including effects associated with fusion-relevant helium and hydrogen generation) are described for research heats of the new steels.