Microstructure refinement and strengthening mechanisms of a 12Cr ODS steel processed by equal channel angular extrusion

Multiscale microstructure refinement of a 12Cr-ODS steel by equal channel angular extrusion (ECAE) was investigated by numerous microscopy techniques. The as-HIPped material showed a bimodal microstructure. Three types of second phase particles, including Y2O3, (Cr, Fe)23C6 and Cr oxide, were observed. After ECAE, the large matrix grains and Cr rich particles were effectively refined, and yttrium oxide nanoparticles surrounding ultrafine grain boundaries were redistributed. Geometry change of nanoscale yttrium oxide particles was also observed. An increased hardening by ∼35% was related to ECAE induced refinement of microstructures.