Physical Properties of Mold Flux and Mineralogical Characteristics of Flux Film for Low-alloy Peritectic Steel Continuous Casting

To meet the demanding requirements of continuous casting for low-alloy peritectic steel, this study aimed to design high-performance mold fluxes with optimized properties. The melting properties, crystallization behavior, mineralogical characteristics, and heat transfer mechanism of the industrial mold fluxes and flux films were investigated by melting tester, viscometer, in situ thermal analyzer, thermal conductivity meter, polarizing microscope, X-ray diffraction, and thermodynamic software. The results demonstrate that mold fluxes suitable for low-alloy peritectic steel possess a narrow melting temperature range, low melting point (<1200 °C), and low viscosity (<0.1 Pa·s) to ensure adequate fluidity and lubrication. A key characteristic of the mold fluxes is strong crystallization ability, reflected by a high critical crystallization cooling rate (>50 °C/s) and high initial crystallization temperature (>1350 °C), facilitating the rapid formation of a stable crystalline layer and uniform heat transfer. The flux films with outstanding characteristics have a multilayered structure and high crystallization ratio (60–80 vol%), predominantly comprising a high fraction of coarsened cuspidine crystals. Further analysis of the heat transfer mechanism reveals that the highly crystalline and coarse-grained microstructure promotes the formation of micropores and crystal boundaries in flux films, which substantially increase thermal resistance, leading to low thermal conductivity (0.47–0.67 W/m·K) and effective control of heat transfer rate. It is concluded that enhancing crystallization performance through optimizing flux composition (boosting Na2O content and basicity) to promote cuspidine formation and tailor crystallinity, is the crucial route for acquiring the desired mineralogical structure of flux films and enabling efficient continuous casting of low-alloy peritectic steel.