Analysis of Oxide Dispersion during Solidification in Ti, Zr-deoxidized Steels

The control of oxide dispersion is one of the most important factors in the newly explored field of study "oxides metallurgy in steels, " utilizing fine oxide particles as heterogeneous nucleation sites for various precipitates. The distribution of oxides in the solidification structure is greatly influenced by interactions between the oxides and the advancing solid/liquid interface as solidification progresses. In order to clarify the behavior of oxides in steels during solidification, unidirectional solidification experiments was conducted. The distribution of oxides was quantitatively analyzed by CMA, and the experimental results were discussed in comparison with a mathematical calculation taking account of microsegregation and precipitation during solidification. In Ti-deoxidized steel, Ti2O3 segregated in the interdendritic region considerably more than calculated. The discrepancy means, that considerable numbers of oxides were rejected to the interdendritic region by advancing solid/liquid interface during solidification. In Zr-deoxidized steel, on the other hand, ZrO2 distributed relatively uniformly, as expected from calculation. The difference between both species of oxides regarding the rejection/entrapment phenomena is most likely due to interfacial energy between the liquid steel and oxide particles.