Crystallization behavior and melt structure of typical CaO–SiO2 and CaO–Al2O3-Based mold fluxes

Crystallization behavior and melt structure of two typical mold fluxes A (CaO–SiO₂-based) and B (CaO–Al₂O₃-based) for casting high-aluminum steel were investigated using double hot thermocouple technology (DHTT), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results suggest that the crystallization temperature of Flux B is higher, and its crystallization incubation time is shorter compared with Flux A. The precipitated phase in Flux A is CaSiO₃, whereas BaAl₂O₄ and Ca₂Al₂SiO₇ form in Flux B. The structure analyses suggest that the degree of polymerization of Flux A is larger than that of Flux B. In addition, the major structural units of Flux A are Si–O–Si, Q₀^Si, Q₁^Si, Q₂^Si and Q₃^Si, but those of Flux B are mainly aluminate (Al–O–Al, Al–O^-), aluminosilicate (Al–O–Si) and silicate units (Q₀^Si, Q₁^Si, Q₂^Si and Q₃^Si). These different melt structures are the main reasons why the precipitated phases in these two mold fluxes are different, and the crystallization ability of Flux A is weaker than Flux B.