Abstract: CaO-Al₂O₃-based mold fluxes have become a research focus due to their inhibition of steel-slag interface reactions. However, the formation of aluminate minerals tends to result in poor metallurgical properties of the mold flux. Na₂O decomposed from industrial raw material sodium carbonate can remedy such flaws, showing favorable application effects. CaO-Al₂O₃-based fluorine-free mold fluxes were prepared using calcium aluminate refining slag as the primary raw material. The soda ash mass fraction (3%-11%) was adjusted via single-factor method to investigate its effects on crystallization kinetics, thermodynamic behavior, and mineral phase evolution. Results showed that as soda ash mass fraction increased from 3% to 11%, the critical cooling rate for crystallization and slag film crystallinity first increased then decreased, while the incubation time exhibited an inverse trend. The initial crystallization temperature remained relatively unchanged. The primary crystalline phases were acicular Ca₃B₂O₆ and glassy microcrystalline Na₂CaAl₄O₈, both showing peak-then-decline trends in content. Optimal crystallization ability and refined mineral phase structure were achieved at 7% soda ash mass fraction.

Key words: CaO-Al₂O₃-based fluorine-free mold flux, soda ash, crystallization behavior, mineral phase structure