In the current study, effects of the substitution of Li2O by Na2O and MnO on the viscosity, crystallization behavior, and heat transfer of mold slags for casting of Cr12MoV steel were investigated using rotational viscometer, high-temperature crystallization apparatus, and water-cooled copper probe. With the substitution of Li2O by Na2O and MnO, the viscosity at 1300 °C changed less and below 0.1 Pa·s, the melting temperature increased from 940 °C to 997 °C and 872 °C to 1077 °C, and the break temperature increased from 945 °C to 1016 °C and 963 °C to 1018 °C, respectively. Similarly, the initial precipitated temperature of Ca3MgSi2O8 as the predominant phase through calculation and XRD measurement increased, and the initial crystallization temperature at the cooling rate of 1 °C/s increased from 899 °C to 998 °C and 931 °C to 993 °C, but the average crystallization rate decreased from 0.0391 to 0.0189 s−1 and 0.0529 to 0.0128 s−1, respectively, which was comprehensively affected by the nucleation formation and crystal growth under different supercooling. With the gradual substitution of Li2O by Na2O and MnO, the thickness of the solid slag film had the tendency to increase from 1.16 mm to 2.03 mm and 1.71 mm to 2.13 mm, the crystallization ratio decreased from 84.6 to 0 pct and 95 to 0 pct, the steady-state heat flux at 60s had the tendency to decrease from 1.09 to 0.89 MW/m2 and 1.04 to 0.90 MW/m2, and the morphological characteristics of the solid slag film changed significantly from the crystal with small size, that with large size to the completely amorphous glassy phase, respectively. Hence, the substitution Li2O by Na2O and MnO would cause the decrease of the depth of the liquid slag pool, the thickness of the liquid slag film, and the heat flux, which deteriorated the lubrication on the solidified shell, but enhanced the control of the heat transfer during continuous casting of the steel to avoid the surface crack formation of Cr12MoV steel slab.
