s Effects of Oxygen Concentration on the Size Distribution of Oxide Particles in ODS Steel

ODS steel normally contains an exceptionally high oxygen concentration owing to oxygen adsorption on the metal powder surfaces, as well as to the contamination during mechanical alloying and consolidation. In this study, the effect of oxygen concentration on the size distribution of oxide particles in ODS steel has been investigated. The oxygen concentration in one ODS steel sample was about 7000 ppm (sample A), while that in the other was controlled to be about 2500 ppm (sample B) by a hydrogen reduction process prior to consolidation. Sample A revealed a much smaller mean grain size (~10 μm) than sample B (~25 μm). Two types of oxide particles, fine YTiO4 (< 30 nm) and coarse Cr-O (>100 nm), were mainly found in both samples. The fine YTiO4 particles in sample A showed a larger mean particle size (15 nm) than those (9 nm) in sample B, while their number density was nearly the same. Coarse Cr-O particles in sample A revealed a much higher number density than sample B. It is thus concluded that the size distribution and grain size of ODS steel can be controlled by a control of the excess oxygen concentration.