Effects of titanium concentration and tungsten addition on the nano-mesoscopic structure of high-Cr oxide dispersion strengthened (ODS) ferritic steels

To study the effects of titanium concentration and tungsten addition on the nano-mesoscopic structure of high-Cr oxide dispersion strengthened (ODS) ferritic steels, the spatial and size distributions, shape, and coherency of the oxide particles in SOC-5 (Fe–15.95Cr–0.09Ti–0.34Y₂O₃) and SOC-P3 (Fe–13.32Cr–1.9W–0.16Ti–0.33Y₂O₃) were studied by diffraction contrast techniques, including weak beam electron microscopy. When the titanium concentration is increased from 0.09 to 0.16 wt.% with 1.9 wt.% W added, the grain size decreases considerably, while the number density and mean size of the oxide particles significantly increases and decreases, respectively. ∼63.5% and ∼96% of the oxide particles in SOC-5 and SOC-P3 (diameter <4.5 nm), respectively, are coherent with the bcc steel matrix. In SOC-5, ∼36% of the oxide particles (4.5–10 nm in diameter) are semi-coherent; misfit moiré fringes are seen across only ∼12% of the oxide particles with misfit moiré fringe spacing of 1.12 nm, indicating the misfit strain is 0.11. However, only ∼4% of the oxide particles in SOC-P3 (4.5–10 nm in diameter) are semi-coherent; misfit moiré fringes are seen across only ∼2% of the oxide particles with misfit moiré fringe spacing of 0.98 nm, indicating the misfit strain is 0.126. The mean misfit strain of coherent oxide particles in SOC-5 is ∼0.017.