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. (C) The Minerals, Metals & Materials Society and ASM International 201