Observations of crystallization in mold slags with varying Al ₂O₃/SiO₂ ratio

The present paper is an investigation into how the Al₂O ₃/SiO₂ ratio in the compositions of mold slags influences the crystallization behavior of molten slags. The experimental work is based upon observing the crystallization events through a Confocal Scanning Laser Microscope equipped with a hot-stage. The study is motivated by the variation in crystallization that might occur in mold slags due to the pickup of alumina during continuous casting of high Al containing TRIP steels. The crystallization temperature was found to increase with increasing Al₂O ₃/SiO₂ ratio, and the crystal morphology was dependent upon the chemical composition and isothermal temperature. The crystallization path was complex, with CaF₂ found to precipitate first, and followed by a second precipitation event. In this second event, the precipitated phase depended on the chemical composition of mold slag and changed from cuspidine to gehlenite as the mass ratio of Al₂O₃/SiO₂ was increased beyond 0.65, and finally Al₂O₃ was observed when the alumina content was 30wt.% (corresponding to a mass ratio of m _Al2O3/m_SiO2=1.42).