Review of non-reactive CaO–Al₂O₃-based mold fluxes for casting high-aluminum steel

Advanced high-strength steels (AHSSs) have been gradually applied to modern auto industry, as they have the advantages of improving the steel strength and lightening the car weight, which not only ensures the safety but also saves the energy. However, the high-aluminum (Al) content in AHSSs may react with SiO₂ in conventional CaO–SiO₂-based mold flux during the process of continuous casting, which leads to the deterioration of the mold flux properties and a poor slab quality. Then, the non-reactive CaO–Al₂O₃-based mold flux was proposed and has been developing for the casting process of high-Al steels, but there are some problems of low consumption and insufficient lubrication that need to be solved. Thus, previous researches on the effect of each component on the properties of CaO–Al₂O₃-based mold flux were systematically summarized, and the situation of plant trials on CaO–Al₂O₃-based mold flux was evaluated. The results indicated that the proposed CaO–Al₂O₃-based mold fluxes could avoid the slag-metal reaction problems; however, the problems of lubrication, crystallization and heat transfer issues still exist. Therefore, tremendous works still need to be conducted for the development of new generation of CaO–Al₂O₃-based mold flux system. The review was performed aiming to provide a technical guidance for designing and optimizing CaO–Al₂O₃-based mold flux system that meets the demand of the continuous casting process of high-Al steels.