Influence of microstructural parameters on the mechanical properties of oxide dispersion strengthened Fe-14Cr steels

The effect of microstructural parameters on the microstructure, tensile properties from room temperature to 800 °C and creep properties at 650 °C has been investigated in a 14%Cr oxide dispersion strengthened (ODS) steel. Combining a control of oxide addition, consolidation route and thermo-mechanical processing, the different parameters of the microstructure have been varied systematically, namely the size and volume fraction of oxide nano-precipitates, the grain size and the dislocation density.The volume fraction of nano-precipitates is shown to influence the tensile strength throughout the temperature range, whereas a change in precipitate size influences only the low temperature behavior. The effect of grain size is shown to be similar to that of precipitation strengthening. A recrystallized microstructure is shown to improve the ductility of the ODS steel while not degrading the strength or creep resistance. The material processed by hot extrusion presents improved strength and reduced creep rate as compared to that consolidated by hot isostatic pressing. This difference is attributed to the long-range internal stress resulting from the high dislocation density, stabilized by the oxide nano-precipitates.A strength model is presented, and validated on every material using the quantitative microstructural parameters obtained by combination of electron back-scattered diffraction, transmission electron microscopy and small-angle X-ray scattering.

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