New high strength ODS Eurofer steel processed by mechanical alloying

A new improved oxide dispersion strengthened (ODS) Eurofer steel was produced by a novel two step mechanical alloying route. Starting from atomized Eurofer powder, two batches of fine and coarse particles with average sizes of ~60 μm and ~120 μm were milled separately after the addition of Ti and nanosized Y2O3. The final blend of the two powder batches was synthetized by hot isostatic pressing (HIP) to obtain a fully dense material with a microstructure characterized by two distinct zones: zones with high density particles (HDPZ) and zones with low density particles (LDPZ). The mechanical properties of the processed material in the as−HIP state and after tempering have been improved significantly compared to various ODS Eurofer and ODS Fe–Cr steels treated by different thermomechanical processing routes (TMP). The stress−strain curve at 600 °C manifested softening while a steady state constant stress was observed at higher temperatures. The stress exponent was two times lower compared to the base Eurofer material; i.e. ~12 vs ~24. Dynamic grain refinement was observed together with ferrite to martensite transformation resulting in an increase in ferrite−martensite interfaces and formation of low angle grain boundaries (LAGBs). Electron back scatter diffraction (EBSD) technique was used to characterize the microstructure and analyze the deformation mechanism. Ultimate Tensile Strength (UTS) as a function of temperature of the new ODS Eurofer in the as−HIP state compared to various steels for similar applications: (a) Eurofer and ODS Eurofer materials (without thermomechanical treatments), (b) high Cr ODS steels (without thermomechanical treatments) and (c) high Cr ODS steels with subsequent thermomechanical treatments. [Display omitted] •New oxide dispersion strengthened Eurofer was produced via mechanical alloying.•The material was formed by high and low density particles zones.•The material exhibited superior properties compared to various ODS steels.•Fragmentation of grains occurred during deformation.•Frequency of ferrite-martensite interfaces increased during deformation.