Evolution of Microstructure and Mechanical Properties of Oxide Dispersion Strengthened Steels Made from Water-Atomized Ferritic Powder

Nano-structured oxide dispersion strengthened (ODS) steels produced from a 410L stainless steel powder prepared by water-atomization was studied. The influences of Ti content and milling time on the microstructure and the mechanical properties were analysed. It was found that the ODS steels made from the Si bearing 410L powder contained Y-Ti-O, Y-Ti-Si-O, Y-Si-O, and TiO2 oxides. Most nanoparticles produced after 80 h of milling were aggregated nanoparticles; however, after 160 h of milling, most aggregated nanoparticles dissociated into smaller individual nanoparticles. Perfect mixing of Y and Ti was not achieved even after the longer milling time of 160 h; instead, the longer hours of milling rather resulted in Si incorporation into the Y-Ti-O rich nanoparticles and a change in the matrix morphology from an equiaxed microstructure to a tempered martensite-like microstructure. The overall micro-hardness of the ODS steel increased with the increase of milling time. After 80 and 160 h, the microhardnesses were over 400 HV, which primarily resulted from the finer dispersed nanoparticles and in part to the formation of martensitic phases. Tensile strength of the 410L ODS steels was comparable with that of ODS steel produced from gas-atomized powder.