Composition Changes of Inclusions by Reaction with Slag and Refractory: A Review

Precise control on inclusions is of great importance for improving steel quality. In secondary refining, three types of inclusion are generally observed in Al-killed steel: Al2O3, MgO·Al2O3 spinel, and CaO–Al2O3 type. Many researchers have reported on inclusions transformed in the routine of Al2O3 → MgO·Al2O3 spinel → CaO–Al2O3 during secondary refining in Al-killed steel. The deoxidizer of Al is intentionally added to the steel, and Al2O3 inclusions are formed as a deoxidation product. However, MgO·Al2O3 spinel and CaO–Al2O3-type inclusions have been observed even without any intentional Mg or Ca addition. Therefore, it is important to clarify the source of Mg and Ca causing MA spinel and CaO–Al2O3-type inclusions formation, in order to control the compositions of the inclusions. Regarding to this phenomenon, a good review was published by Park and Todoroki in 2010. Several studies have since been conducted. This paper summarized the research activities on the composition changes of inclusions during secondary refining from the aspect of thermodynamics and kinetics.