Evaluation of mechanical properties and nano-meso structures of 9–11%Cr ODS steels

•We successfully manufactured 11Cr-ODS steels with residual α-ferrite controlled.•Dispersion conditions of nano oxide particles were quantitatively characterized.•Tungsten solid solution could improve only tensile strength of ODS steels at 973 K.•Oxide dispersion strengthening was dominant in creep strength of ODS steels at 973 K.

This study carried out mechanical tests and microstructural characterizations of several 9Cr and 11Cr-ODS tempered martensitic steels. From those results, the appropriate chemical composition range of 11Cr-ODS tempered martensitic steel was discussed from the viewpoint of high temperature strength improvement. It was shown that the residual α-ferrite fraction in 11Cr-ODS steel was successfully controlled to the same level as the 9Cr-ODS steel, which has excellent high temperature strength, by selecting the chemical compositions on the basis of the multi-component phase diagram. The tensile strength decreased with decreasing W content from 2.0 to 1.4 wt%. On the other hand, creep strength at 973 K did not degrade by the decreasing W content. Both tensile strength and creep strength increased with increasing population of the nano-sized oxide particles. Small angle X-ray scattering analysis revealed that titanium and excess oxygen contents were key parameters in order to improve the dispersion conditions of nano-sized oxide particles.