Using various methods of physical and chemical analysis, a study was made of phase and chemical transformations in slag-forming mixtures used in the continuous casting of steel and processing of steel in a bucket over a wide range of temperature changes. Data are obtained on the ratio of exo-and endothermic effects, the duration of formation of silicates and slag melt. Based on an improved methodology that allows for the influence of sources and sinks of heat in the heated material, the thermal diffusivity coefficients were determined. Using the coefficients of thermal diffusivity found and the previously determined heat capacity and density, the dependence of the coefficient of thermal conductivity of slag mixtures on temperature was found. The results obtained in the work allow us to predict the technical and economic indicators (including heat inputs) of the use of slag mixtures both at the stage of the choice of starting materials in the preparation of pellets and in the casting of steel.