Effect of CaO/SiO2 and Al2O3/SiO2 Mass Ratios on Structure and Viscosity of Mold Flux for Continuous Casting High-Mn High-Al Steel

During continuous casting process of high-Mn high-Al steel, soluble Al in the steel typically reacts with SiO2 in the mold flux, resulting in a decrease in SiO2 content and an increase in Al2O3 contents in the flux. The structure of slags with varying CaO/SiO2 and Al2O3/SiO2 mass ratio is investigated using Raman spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. In the deconvolution results of Raman and NMR spectra, it is shown that the relative fractions of Q(Si)(0) and Q(Si)(1) significantly increase, while Q(Si)(2) and Q(Si)(3) gradually decrease with an increase in the CaO/SiO2 mass ratio from 0.52 to 1.02, resulting in depolymerization of the bridge oxygen structure. The silicon-oxygen tetrahedron transforms into aluminum-oxygen tetrahedron when the Al2O3/SiO2 mass ratio increased from 0.05 to 1.01. The viscosity of the slags with varying composition from 1573 to 1373 K is investigated. In the results, it is shown that with an increase in the CaO/SiO2 mass ratio, the viscosity decreases, and the complex Si-O network structure is depolymerized. The viscosity decreases first as the Al2O3/SiO2 mass ratio increases from 0.05 to 0.24 and then increases as the mass ratio from 0.24 to 1.01, with the network formers transfer from Si-O to Si-Al-O structures.