Non-isothermal Crystallization Kinetics of Mold Fluxes for Casting High-Aluminum Steels

This paper investigates the crystallization behavior of CaO-SiO₂- and CaO-Al₂O₃-based mold fluxes for casting high-aluminum steels using single hot thermocouple technology, developed kinetic models, and scanning electron microscope. The results showed that the crystallization ability of the typical CaO-SiO₂-based Flux A (CaO/SiO₂ 0.62, Al₂O₃ 2 mass pct) is weaker than that of CaO-Al₂O₃-based Flux B (CaO/SiO₂ 4.11, Al₂O₃ 31.9 mass pct) because of its higher initial crystallization temperature. The crystallization kinetics of Flux A was "surface nucleation and growth, interface reaction control" in the overall non-isothermal crystallization process, whereas that of Flux B was "constant nucleation rate, 1-dimensional growth, diffusion control, in the primary crystallization stage, and then transformed into constant nucleation rate, 3-dimensional growth, interface reaction control in the secondary crystallization stage." The energy dispersive spectroscopy results for Flux B suggested that the variations in the crystallization kinetics for Flux B are due to different crystals precipitating in the primary (BaCa₂Al₈O₁₅) and secondary (CaAl₂O₄) crystallization periods during the non-isothermal crystallization process.