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Abstract: Ferritic–martensitic (F–M) steels with 9wt.%Cr are important structural materials for use in advanced nuclear reactors. Alloying composition adjustment, guided by computational thermodynamics, and thermomechanical treatment (TMT) were employed to develop high strength 9Cr F–M steels. Samples of four heats with controlled compositions were subjected to normalization and tempering (N&T) and TMT, respectively. Their mechanical properties were assessed by Vickers hardness and tensile testing. Ta-alloying showed significant strengthening effect. The TMT samples showed strength superior to the N&T samples with similar ductility. All the samples showed greater strength than NF616, which was either comparable to or greater than the literature data of the PM2000 oxide-dispersion-strengthened (ODS) steel at temperatures up to 650°C without noticeable reduction in ductility. A variety of microstructural analyses together with computational thermodynamics provided rational interpretations on the strength enhancement. Creep tests are being initiated because the increased yield strength of the TMT samples is not able to deduce their long-term creep behavior. [Copyright &y& Elsevier]

Abstract: Mechanically alloyed, oxide dispersion strengthened (MA/ODS) ferritic alloys are attractive for fusion reactor applications because of their potential for operation at high temperatures and also because the dispersed oxide particles may provide a trap for transmutant helium. The microstructural stability of MA/ODS Fe–14wt% Cr–3% W–0.4% Ti–0.3% Y2O3 ferritic alloys was investigated by atom probe tomography. Atom probe tomography revealed that these MA/ODS 14YWT ferritic alloys contain a high number density of nanometer scale titanium-, yttrium- and oxygen-enriched nanoclusters in the as-extruded condition. These nanoclusters were found to be extremely resistant to coarsening at temperatures of at least 1000°C. [Copyright &y& Elsevier]