Insight into compositional dependence of thermophysical properties and structure of Al2O3-SiO2-CaF2-CaO-Li2O melts

Low-fluoride-lime Al2O3-SiO2-CaF2-based slag melts were designed for producing sulfur-bearing free-cutting steels by electroslag remelting. These newly designed slags must maintain the technological parameters, related to viscosity and crystallization characteristics. The structure, viscosity and crystallization of the slag with different CaO/SiO2 mass ratios and Li2O contents were studied. Raman spectroscopy shows that the silicate network is depolymerized and the aluminate network is polymerized as CaO/SiO2 mass ratio or Li2O content is increased. 27Al MAS-NMR spectra demonstrates the presence of small amounts of AlV and AlVI species in the melts with 0 mass% and 1.18 mass% Li2O, whereas Al is present exclusively in AlIV in other cases. The measured viscosity of the melts and the apparent activation energy of viscous flow decrease with increasing CaO/SiO2 mass ratio or Li2O content. Both the crystallization temperature and the crystallization ability of melts increase with increasing CaO/SiO2 mass ratio or Li2O content.