The role of slag in the process of continuous casting of steel (CCS) is reduced to the thermal and chemical insulation of the liquid steel surface, and additionally to refining. The ability to adsorb non-metallic inclusions flowing off from the crystallizer, mainly Al2O3, determines its physicochemical properties. As a result of adsorption and dissolution of inclusions tin he liquid layer the viscosity and thickness of mould flux change, which eventually affects the technological parameters and behavior of slag in the crystallizer. The influence of aluminum oxide on the viscosity of slag was empirically investigated with a structural viscosity model worked out by Nakamoto. The results of the simulation are presented in the form of plots. Authors observed a significant influence of Al2O3 on the slag viscosity, which suggests that this effect should be taken into account when selecting chemical composition of mould flux for definite types of steel. The results of calculations also show that the disturbances in casting caused by the use of the mould slag may be connected with the content of non-metallic inclusions in steel.
Filtration is one of the most efficient methods of removing Al2O3 inclusions from liquid steel. The efficiency of this process depends on the physicochemical parameters of liquid metal, inclusion and properties of the applied filters. The particles attracted during filtration undergo agglomeration, collisions and chemical reactions on the filter surface, with the emphasis on the mechanism of particle collisions and the role of material from which the filter was made. The aluminum oxide inclusions collide with the filter surface and as the growing process continues, the particles also collide with the previously adsorbed inclusions. At the interface of particle and filter the mixing of the metal bath is most intense, being a result of a sudden change of flow direction and breaking up the stream of liquid metal which is in a direct contact with material. The efficiency of filtration is defined not only by the behavior of individual particles but of all population. The simulations revealed that only a small fraction of these particles adheres directly to the filter material; most of them stick to the former ones. Attention should be also paid to the fact that some of the inclusions which contacted the filter walls do not form a permanent connection and are then entrained by metal. Authors solved the problem of agglomeration and collisions of Al2O3 inclusions with the ceramic surface of the filter with the PSG method, mainly used for the analysis of agglomeration of inclusions during steel refining in the ladle.
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