EFFECT OF COOLING RATE ON OXIDE PRECIPITATION DURING SOLIDIFICATION OF LOW-CARBON STEELS

Effect of cooling rate on oxide precipitation during solidification was investigated using Ti and Al-Ca deoxidized low-carbon steels. The number and size distribution of oxides in the continuously cast steels have been observed and theoretically analyzed. The results obtained are as follows. The Ti deoxidized steel has more soluble oxygen before solidification than the Al-Ca deoxidized steel. With the increase in the cooling rate during solidification, the number of oxides increases and the size becomes smaller in the Ti deoxidized steel. During the solidification, segregation makes oxygen content increase above the equilibrium value with oxide in Ti deoxidized steel. The difference between the oxygen content increased by segregation and that in equilibrium is a driving force for the oxide growth. With increasing cooling rate, time for oxide growth decreases and supersaturation of oxygen for oxide precipitation increases. Consequently, the number of the oxide increases by the increase in the frequency of precipitates during solidification for high cooling rate.