Evolution of compositions and properties of CaO-SiO2 based mold flux for continuous casting high Mn steel

Abstract

In order to investigate the interfacial reaction phenomena between the continuous casting molten steel with high Mn content and CaO-SiO2 based mold flux, a series of laboratory experiments were carried out. Various factors which may affect the composition evolution in mold flux were taken into account to propose a reaction mechanism. Based on the results obtained experimentally, four types of mold flux representing different stages of composition evolution were used to elucidate lubrication and crystallization behaviors of mold flux during the reaction process. The results show that the chemical reaction, 2[Mn] + (SiO2) = [Si] + 2(MnO), is mainly governed by the Mn content in molten steel. The initial (CaO/SiO2) in mold flux has a moderate effect on this reaction. The couple effect of MnO accumulation and SiO2 reduction induces a remarkable decline in viscosity and break temperature of mold flux. Crystallization temperature shows a downward trend after the first rise. The formation of Ca4Si2O7F2 takes place first in all mold flux samples. The morphology of cuspidine changes from small faceted shape with regular spacing to larger interconnected block, and the number of cuspidine crystals decreases with MnO accumulation and SiO2 reduction. In mold fluxes with higher MnO content, the micro tephroite crystals precipitate at lower temperature, while the crystallization of CaF2 is suppressed, which results in higher heat flux and thinner solid slag film. The findings in this study provide the evidence of heat transfer deterioration in flux layers during the continuous casting process for high Mn steel.