Use of Synthetic Slags to Control the Level of Inclusions in Steels

The presence of inclusion in the steels plays a strong role in the steel product quality, so it is very important to have a deep insight into the behavior of inclusions in the continuous casting. The studies of processes for searching steels with high level of cleanliness are a concern that has being done around the world in steelmaking industry for many decades. All in all, the phenomena that controls inclusions on steels are highly complex. It is well established that the during the deoxidation of steels, the formation of non-metallic inclusions occurs, and the presence of them causes several problems both in the production stages and in the final mechanical properties of the steel produced. Therefore, due to these problems, inclusions should be removed from steels when possible [1]. According to the literature [1-3] the removal of inclusions occurs in three stages. In the first one, called flotation, the inclusion is transported to the steel/slag boundary. In the second one, designed as separation, occurs the rupture of the surface tension of the steel allowing the arrival of the inclusion to the slag. Finally, the third and last step is the dissolution which is the most important, particularly for solid inclusions that have limited solubility in slag and are therefore very sensitive to the physical and chemical characteristics, temperature gradients and the volume of the slag. Results obtained by Choi et al [1] and used by Reis et al [4] highlight that the reduction of slag viscosity favors the dissolution of alumina being its influence more important than the thermodynamic potential for dissolution as shown in Figure 1.