Ladle treatment of steel by slag-forming mixture calls for optimal proportions of the components and optimal physicochemical and thermochemical properties of the mixture. Essentially, the slag-forming mixture is a multicomponent fine-grain system with the following functions:
- protection of the steel from secondary oxidation;
- heat insulation of the metal meniscus in the ladle;
- assimilation of the nonmetallic inclusions from the steel;
- prevention of the formation of a slag crust in casting.
The specified properties of the slag-forming mixture include the viscosity, softening temperature, melting point, thermal conductivity, and density. These properties may be regulated by selecting the chemical and phase composition of the mixture. The composition of the slag-forming mixture for the ladle treatment of steel with the necessary properties is selected on the basis of the oxide system Al2O3– MnO–SiO2, taking account of the nonmetallic inclusions formed in the steel on reduction. We know that, for most nonmetallic inclusions, the reaction products are associated with reduction and alloying of the steel; they are mainly oxides of aluminum, silicon, and manganese [1]. Correspondingly, the density of the nonmetallic inclusions is about two or three times less than that of the steel. That facilitates the free circulation of the nonmetallic inclusions with convective fluxes in the metal and their unobstructed entrainment to the metal–slag boundary, where they are partially assimilated by the slag [2]. The effectiveness with which the slag coating assimilates nonmetallic inclusions largely depends on the affinity of the corresponding phases.
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