Microstructures and mechanical properties of 9Cr oxide dispersion strengthened steel produced by spark plasma sintering

Highlights: • A 9Cr-ODS steel was produced by mechanical alloying and spark plasma sintering. • Bimodal grain size distribution was observed. • Formation mechanism of bimodal grain size distribution was discussed. • The size and number density of nanoscale particles were obtained by SAXS and HRTEM. • The contribution of nano-sized particles to yield strength is dominating. - Abstract: 9Cr oxide dispersion strengthened (ODS) steel was fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The nano-sized particles, grain size distribution and mechanical properties of 9Cr-ODS steel sintered at 950 °C were studied by synchrotron radiation small angle X-ray scattering (SAXS), high-resolution transmission electron microscopy (HRTEM), electron backscatter diffraction (EBSD) and tensile experiment. The results showed that bimodal grain size distribution in the matrix is observed, which is attributed to the heterogeneous recrystallization process during the SPS. High-density nano-sized Y₂Ti₂O₇ and some large oxides of Cr₂Mn(Ti)O₄ are formed in 9Cr-ODS steel. The number density and average size of Y₂Ti₂O₇ obtained from SAXS are 4.72 × 10²²/m³ and 4.4 nm, respectively. The yield strengths of 9Cr-ODS steel fabricated by SPS are compared with the typical 9Cr-ODS steel produced by HIP.