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

Effect of cooling rate on oxide precipitation during solidification wa s investigated using Ti and Al-Ca deoxidized low-carbon steels. The nu mber and size distribution of oxides in the continuously cast steels h ave been observed and theoretically analyzed. The results obtained are as follows. The Ti deoxidized steel has more soluble oxygen before so lidification than the Al-Ca deoxidized steel. With the increase in the cooling rate during solidification, the number of oxides increases an d the size becomes smaller in the Ti deoxidized steel. During the soli dification, segregation makes oxygen content increase above the equili brium 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, t ime for oxide growth decreases and supersaturation of oxygen for oxide precipitation increases. Consequently, the number of the oxide increa ses by the increase in the frequency of precipitates during solidifica tion for high cooling rate.