Review on interaction between slag, steel and inclusions in secondary steelmaking

The refining function of slags in ladle metallurgy comprises of desulphurization and capture of inclusions, which are removed from the steel melt in the course of deoxidation procedure. In that task, the interaction between the two phases, slag and steel is active and highly beneficial. Further, the slag has a passive, shrouding role when it protects steel from atmospheric oxidation and heat losses. In some cases, slag can even have negative influences as a reoxidation source and eventual origin of harmful inclusions in steel. Conventionally, inclusions in steel are understood as deoxidation products, remained in the steel after the deoxidation process. These, “intrinsic” inclusions are then related to the steel composition i.e. determined by the deoxidizing components in steel, generally Al but even Si, Mn and Ca. However, in intensive ladle treatment the role of the top slag is not only the receiver of inclusions from the steel but pronounced chemical interaction between the liquid slag and metal can take place. Consequently, a component with low activity in the slag e.g. SiO2 can intensify deoxidation by silicon. By contrast, CaO has a high activity in basic ladle slags and it can interact with steel and bring CaO into inclusions. As a consequence, the type of inclusions can remarkably change. The current paper examines the fundamentals of interaction phenomena between slag, steel and inclusions via thermodynamic calculations, experimental results from steel industry, and observations on related research in the literature.Peer reviewe