The melting point and volatilization characteristics of a fluorine-containing slag were investigated under different heating rates and premelting processes. The “hemisphere method” was used to detect the melting point, and the results showed that the measurements for the fluorine-free slag increased with increasing heating rate, and the deviation reached 60 °C and was affected by the hysteresis and fractional melting. The measured values and volatilization of the fluorine-containing slag decreased with increasing heating rate. The weight loss reached 16.8%, and the melting point deviation reached 90 °C, which was primarily affected by the volatility. The melting point of the synthetic fluorine-containing slag was 70 °C higher than that of the premelted slag due to flux volatilization of 8.3%. Scanning electron microscopy-energy dispersive spectroscopy revealed a large amount of CaF2 on the surface of the melted slag. The internal crystals in the synthetic slag were mainly diamond-shaped calcium fluoroaluminate (3CaO·3Al2O3·CaF2) and those in the premelted slag were needle-shaped cuspidine (3CaO·2SiO2·CaF2) that formed during secondary crystallization. Two factors that impacted the volatilization were proposed: one is the content of free CaF2, and the other is the slag structure. Based on these factors, volatilization models for synthetic and premelted fluorine-containing slags were established. This work is of significance for relevant measurement specifications to ensure the repeatability and comparability of the physicochemical properties, especially for volatile-containing slags.

It was taken as typical steelmaking fluorine-containing slag systems with the remelting electroslag, continuous casting mould flux and refining slag. The volatilization behaviour of each slag system was analysed by thermogravimetric (TG) and mass spectrometry (MS) detection. The results showed that the remelting electroslag volatilized significantly above 1300°C and the volatiles were mainly CaF 2 , MgF 2 with a small amount of SiF 4 and AlF 3 ; the continuous casting mould flux volatilization was divided into two stages, in the first stage (500°C∼800°C), CaF 2 and Na 2 O reacted to form NaF, and in the second stage (greater than 1200°C), the CaF 2 evaporation was highlighted; for CaF 2 -CaO-based refining slag, the volatilization was the most significant at the eutectic point 84% CaF 2 –16% CaO, and the volatility can be reduced by adding 5% SiO 2 . This research will be guiding significance for the composition and performance control of fluorine-containing slag and metallurgical environmental protection in the steelmaking process.

A viscosity estimation model for fluorine-containing mold flux for continuous casting was investigated based on the Arrhenius formula and the rotating cylinder method combined with nonlinear regression analysis. This model is highly applicable and not limited by the slag of a certain composition. For most slag compositions, the viscosities estimated with this model deviated from the measured values by no more than 10%, which was in better agreement with the measured values than the viscosities estimated by the Riboud, Iida and Mills models. According to the model calculation and experimental detection, a viscosity isogram of CaF2-Na2O-Al2O3-CaO-SiO2-MgO slag was produced, and the mass fraction of CaF2 in the low-viscosity zone was nearly 14%. An X-ray fluorescence spectrometric analysis of slag after the viscosity test showed that CaF2 and Na2O were significantly reduced, and the measured viscosity was greater than the theoretical viscosity due to the volatilization.