Effect of thermomechanical treatment on 9Cr ferritic–martensitic steels

High-Cr (9 wt.%) ferritic–martensitic steels are important materials for use in nuclear reactors. This study shows a development activity for this category of steels via thermomechanical treatment (TMT) optimization and alloying element adjustment based on Grade 92 steels. Vickers microhardness and tensile tests were employed to assess the mechanical properties of the materials in the normalized-tempered (N&T) and optimized TMT conditions. The treatment of one of the modified heats produced ∼29% and ∼47% increases in hardness and yield strength, respectively, compared to the Grade 92 in the N&T condition. The TMT-treated alloys showed comparable or superior strength relative to the oxide-dispersion-strengthened steel PM2000. Microstructure analyses by optical and transmission electron microscopy together with thermodynamic calculations identified the strengthening mechanisms of the TMT and precipitates.