Constitutional Segregation of Al^sub 2^O3 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 Al^sub 2^O3 pickup in slag varies approximately from 7 to 12 pct and depends on the slag basicity. Significantly higher Al^sub 2^O3 pickup reported in basic slags and polynomial relationship exists between them. The effect of chemical composition on microstructure evolution and Al^sub 2^O3 partitioning during crystallization was identified in all three types of mold slags. The microsegregation of Al^sub 2^O3 inclusions in the constituent phase of CaO-SiO2-Al^sub 2^O3 based slag film is presented. Constitutional segregation of Al^sub 2^O3 inclusion in slag was found to affect the Al^sub 2^O3 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 Al^sub 2^O3 inclusion partitioning and interdendritic segregation in the mold slag is studied with metallographic evidence.[PUBLICATION ABSTRACT]