Development of a novel ZrO₂ dispersion strengthened 9Cr ferritic steel: Characterization of milled powder and subsequent annealing behavior

A novel ODS ferritic steel with ZrO₂ dispersoids is developed as a candidate structural material for future fast reactor applications. Encouraged by our earlier results demonstrating the retention of crystallinity by ZrO₂ dispersoids during milling, the 9Cr ODS steel powder has been synthesized under optimized ball milling conditions and subsequently characterized. The analysis of milled powder showed fine dispersions of ZrO₂ with a size range of 2–10 nm. Upon annealing at 1223 K, precipitation of non-stoichiometric FeO was observed along with fine ZrO₂ dispersoids. All the constituent phases are identified using Synchrotron XRD, Conventional and HRTEM. An excellent thermal stability has been manifested by the dispersoids as it retained its fine structure during the annealing treatment with ~ 95% of dispersoids measuring < 11 nm. Additionally, ~ 95% of the FeO precipitates are shown to be < 16 nm in size, indicating itself as a strong precipitation strengthener to the material. This two-fold strengthening by ZrO₂ dispersoids and FeO precipitates, along with nanostructured matrix is believed to play the major role in the high-temperature strength of the material being developed and it could lead to the development of a new generation ODS steel.