Reactivity and thermo-physical properties of MnO-modified CaO-Al2O3-based mold fluxes for advanced high-strength steels

Abstract

Advanced high-strength steels (AHSS) with superior strength, formability and ductility meet the new demand for balancing vehicle performance and passenger safety in the automotive industry. AHSSs are typically alloyed with substantial amounts of Al and Mn. However, during continuous casting, the alloying elements may react with the conventional CaO-SiO2-based mold fluxes and cause significant compositional changes, leading to deterioration of mold fluxes and surface defects of steel plates. In this study, the CaO-Al2O3-MnO-based mold fluxes were investigated based on CALPHAD-type thermodynamic calculations and kinetic modeling based on the local equilibrium model as well as high-temperature in situ interfacial reactions at 1600 °C. Furthermore, viscosity measurements and thermal analyses were performed to evaluate the thermo-physical properties of the CaO-Al2O3-MnO-based mold fluxes. The simulations agreed closely with experiments, suggesting the interfacial reactions were diffusion-controlled. While MnO in the mold fluxes participated in the redox reactions with Al in molten steels, its addition could lower the break temperature, viscosity, and liquidus temperature of mold flux without too severe reactions at the initial stage. The CaO-Al2O3-MnO-based mold fluxes are promising for continuous casting of high-Mn high-Al steels.