Effect of Basicity on the Melting Characteristics, Phase Transformation Behavior, and Heat Release of Blast Furnace Slag

The regulation of basicity is crucial for the blast furnace slagging regime. In light of the fluidity, melting properties, and exothermic characteristics of blast furnace slag, this study investigates the effects of binary basicity ( R 2 = CaO/ SiO 2 ) ranging from 0.95 to 1.40 on the fluidity, melting behavior, phase evolution, and heat release of a CaO–SiO 2 –Al 2 O 3 –MgO (CSAM) quaternary slag system through high‐temperature viscosity experiments and FactSage thermodynamic calculations. The results indicate that the slag viscosity exhibits a nonlinear trend with increasing R 2 , and the influence of R 2 on viscosity varies between low‐ and high‐temperature regimes. The difference between the melting temperature ( T M ) and the liquidus temperature ( T L ) increases with rising R 2 , indicating that high‐basicity slags maintain a “solid–liquid coexistence” state over a wider temperature range. Variations in R 2 significantly affect the composition of precipitated solid phases: melilite predominates when R 2 < 1.2, while the proportion of Ca 2 SiO 4 increases notably when R 2 > 1.3. At R 2 = 1.35, the system approaches the eutectic point. Heat release calculations reveal that, owing to the eutectic reaction of the slag, the R 2 = 1.35 slag exhibits the highest latent heat release efficiency in the temperature range from 1500°C to T M .