Design of Reduced Activation Ferritic/Martensitic Steels by Multiphase Optimization during the Entire Processing

Abstract

Improving the mechanical properties of reduced activation ferritic/martensitic (RAFM) steels has been a long-standing challenge that inhibits the construction of fusion engineering test reactors. To increase the toughness of RAFM steels without sacrificing too much strength, a modified RAFM steel was designed by optimizing multiple phases, including M₂₃C₆, MX, and martensite blocks; the combination of the composition and the entire thermomechanical processing scheme was also considered. To improve the composition, thermodynamic calculations were used to tailor the precipitation fraction. To optimize the thermomechanical treatment and heat treatment, a modified thermomechanical control process and intermediate heat treatment were employed to refine both the precipitation and martensite blocks. The experimental results for the microstructure and mechanical properties showed that, compared with that of CNA1 and EUROFER97, the newly designed RAFM steel had a more rational microstructure and greatly improved toughness with sufficient strength. The strengthening was quantitatively analyzed by Olson’s strengthening model to guide the additional development of modified RAFM steels.