The composition of fluoride‐containing mold fluxes changes when their melting point or viscosity are measured because the fluoride in the mold fluxes evaporates at high temperatures. Therefore, the measured melting points and viscosities are not those of the original fluxes, and thus, the results are not accurate. Therefore, evaluating the effects of evaporation is essential to accurately investigate the relevant properties. Herein, the chemical composition of the slag is determined using thermogravimetric analysis (TGA), roasting tests, and evaporation mechanism after the physical properties of the slag are measured using conventional methods. The measured melting point and viscosity are then matched with the modified slag composition instead of the original composition. This method is applied to different fluoride‐containing mold fluxes. The weight of the mold fluxes is reduced by more than 10% during the measurements, indicating that a large amount of the volatiles react and evaporate. The actual flux compositions corresponding to the observed melting point or viscosity of the mold fluxes are obtained through roasting test and TGA; therefore, one can easily match the measured mold flux properties to the flux composition. This study will help in determining other physical properties of slag and other melts containing volatiles.

In hemisphere point temperature (Thp) measurement of continuous casting mold flux, the evaporation of volatiles under high temperature will have a strong impact on the results. Based on the comprehensive analysis of hemisphere point method and its influencing factors, the corresponding volatile-containing mold flux and non-volatile mold flux were selected to get Thp with different heating rates. Combined with the Thp measurement and TG-DSC results, the effect of relevant factors during measuring process were analysed and the way to characterize and evaluate the effects were suggested. Furthermore, an improved method of mold flux melting point test was put forward. The results showed that for non-volatile mold flux, the temperature hysteresis has a greater effect than heat transfer delay and fractional melting. And for mold flux with volatile, the effect of evaporation is greater than other factors. Traditional hemisphere-point method is no longer suitable for the volatile mold flux. In order to get through this problem, improved methods were proposed. One is measuring Thp by traditional way, correcting the composition at the Thp, corresponding Thp with the corrected composition. Another is taking the initial composition, revising the hemispherical point temperature Thp, matching the revised Thp with the initial composition.