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 AlO pickup in slag varies approximately from 7 to 12 pct and depends on the slag basicity. Significantly higher AlO pickup reported in basic slags and polynomial relationship exists between them. The effect of chemical composition on microstructure evolution and AlO partitioning during crystallization was identified in all three types of mold slags. The microsegregation of AlO inclusions in the constituent phase of CaO-SiO-AlO based slag film is presented. Constitutional segregation of AlO inclusion in slag was found to affect the AlO 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 AlO inclusion partitioning and interdendritic segregation in the mold slag is studied with metallographic evidence.