Developing novel high-Si 12 % Cr reduced-activation ferritic/martensitic cladding alloys via the cluster-formula approach and CALPHAD method

The corrosion-resistance in lead–bismuth eutectic (LBE) coolant at elevated temperatures of traditional reduced-activation ferritic/martensitic (RAFM) steels could not meet the requirements for the application of fuel claddings. Here, we designed four series of high-Cr/Si RAFM alloys via the cluster-formula approach and CALPHAD method, in which the combinations among alloying elements were tuned to investigate their influences on the martensitic matrix and precipitated phases. Three novel alloys were selected for further experimental verification. These alloys with heterostructures containing few ferrites in martensitic matrix possess high yield strength (423 ∼ 523 MPa at room-temperature, 240 ∼ 297 MPa at 823 K) and excellent strain-hardening ability, where the strengthening mechanisms were also discussed. The corrosion measurements in LBE at 773 K for 1000 h indicated that these alloys with trace amount (<3 %) of ferrite, especially the Al-containing alloy (Fe-11.3Cr-0.26 V-0.13Ta-1.3 W-1.0Si-0.22C-0.2Al-0.4Mn), possess prominent corrosion-resistance (∼ 2 μm oxide scales), much better than the commercial EP823 (∼ 22 μm). Moreover, this alloy has outstanding creep-resistant property, where the rupture lifetime under the extreme condition of 923 K/90 MPa is more than twice that of EP823. The present work provides a new strategy to efficiently develop novel high-Cr/Si RAFM alloys for nuclear application.