EFFECT OF THE COOLING RATE ON COMPOSITIONS OF THE OXIDES PRECIPITATED DURING SOLIDIFICATION OF STEELS

Effect of the cooling rate on composition of oxides precipitated during solidification was investigated using Ti deoxidized steel. The composition and size of oxides in the continuously cast steels have been observed and theoretically analyzed. The results obtained are as follows. The oxide mainly consists of Ti2O3, Al2O3 and MnO. The composition of oxide whose diameter is less than about 10 mu m changes with cooling rate during solidification. The Ti2O3 content increases and Al2O3 content decreases with the decrease in the cooling rate. On the other hand, the composition of oxide whose diameter is more than about 10 mu m does not change with cooling rate. When the size of oxide is smaller, the effect of cooling rate on oxide compositions is remarkable. As a result of the theoretical analysis of the oxide behavior during solidification on the basis of a diffusion growth model, it has been found that the increase in the diameter of oxide which grows during solidification is larger when the size of oxide before solidification and the cooling rate during solidification are smaller. The Ti2O3 content increases with the decreases in the diameter of oxide before solidification and in the cooling rate. The theoretically estimated results on the changes in compositions and diameter of oxides during solidification of steel qualitatively agree with the observed results.