Melting Behavior of Mold Flux with Exothermic Components for High-Speed Continuous Casting

The effects of exothermic additives on the melting behavior of mold flux were systematically investigated using a heating microscope, FactSage thermodynamic simulations, thermogravimetry–differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. Results indicate that the addition of exothermic agents shortens the melting time of mold flux. Compared with Ca–Si alloy, Si exhibits superior combustion performance due to its higher theoretical combustion enthalpy, although it also increases the initial melting temperature. An endothermic event between 530 °C and 650 °C is associated with the Ca₂B₂O₅ phase transition, while an exothermic peak from 650 °C to 950 °C is attributed to the formation of wollastonite due to solid-state reaction of CaO and SiO₂ after combustion of exothermic agents. A further exothermic event between 1100 °C and 1375 °C corresponds to the polymorphic transformation of wollastonite into calcium metasilicate. Mechanistic analysis reveals that there are two dominant pathways enhancing flux melting: (1) heat releases from the combustion of exothermic agents (e.g., Si releasing 3041 J g⁻¹) and (2) additional heat generates during the wollastonite-to-calcium metasilicate transformation. These findings provide new insights into designing fast-melting mold fluxes for high-speed continuous casting.