Constitutional Segregation of Al₂O₃ in Mold Slag and Its Impact on Steel Cleanliness During Continuous Casting

The alumina pickup in a range of mold fluxes used for continuous casting of aluminum (Al)-killed ultralow carbon, low carbon, and peritectic steel have been measured. The Al₂O₃ pickup in slag varies approximately from 7 to 12 pct and depends on the slag basicity. Significantly higher Al₂O₃ pickup reported in basic slags and polynomial relationship exists between them. The effect of chemical composition on microstructure evolution and Al₂O₃ partitioning during crystallization was identified in all three types of mold slags. The microsegregation of Al₂O₃ inclusions in the constituent phase of CaO-SiO₂-Al₂O₃ based slag film is presented. Constitutional segregation of Al₂O₃ inclusion in slag was found to affect the Al₂O₃ pickup phenomena during continuous casting. Segregation of alkalis like Na and K was also observed in an Si-rich interdendritic matrix, whereas F was retained in the dendrites of all the slags studied. The Al₂O₃ inclusion partitioning and interdendritic segregation in the mold slag is studied with metallographic evidence.