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An attractive way to enhance the ductility of ODS ferritic steels is to develop an alloy with a bimodal grain size distribution, in which the micron-sized coarse grains provide high ductility. The nanometer-sized fine grains enhance the tensile strength. The microstructures were obtained by blending the gas-atomized powders and mechanical alloyed powders, followed by hot forging and annealing. The homogeneously distributed nanometer-sized oxide nanoparticles can also be detected. Mechanical properties tests revealed a great improvement in ductility in comparison with other ODS ferritic steels, and high strength over the whole range of test temperatures, owing to the fine grains and oxide nanoparticles. The combination of high ductility and high strength makes this ODS ferritic steel much promising in high-temperature application.

The effect of vacancy on the microstructure of the ferritic steel with a nominal composition of Fe–14Cr–3W–0.4Ti–0.4Y 2 O 3 was investigated. By using the resistivity measurements, the vacancy formation enthalpy of the alloy is calculated to be 1.11 ± 0.16 eV, which is lower than that of α-Fe. The Ti–Y–O nanoclusters in the alloy are responsible for stabilizing the vacancies. The hardness of the steel increases with the heat treating temperature. The hardening mechanism in the ferrite matrix can be attributed to the interaction between dislocations and vacancies or vacancy clusters.