Effect of post annealing on microstructure and mechanical properties in Ni-free N-containing ODS steel

Abstract

Abstract The precipitation behavior of Y2O3 and MnO nanoparticles after isothermal treatment, in a Ni-free N-containing oxide dispersion strengthened (ODS) steel was studied by wide-angle X-ray scattering (WAXS), ultra-small-angle and small-angle X-ray scattering (USAXS/SAXS), small angle neutron scattering (SANS) and scanning transmission electron microscopy (STEM). Mechanical properties were investigated via tensile and micro-hardness testing. Additional precipitation occurred during annealing, in addition to the precipitates formed during sintering. The highest volume distribution of Y2O3, with average size of 6\u202fnm, was determined by alloy contrast variation (ACV) analysis of SAXS and SANS for the sample annealed at 800\u202f°C; this sample shows the highest hardness and ultimate tensile strength. Above that temperature, coarsening of both matrix and precipitates and depletion of nitrogen from matrix degraded the mechanical properties. The very fine nanoparticles and thermally induced dissolution of nitrogen influenced mechanical properties.