Mineralogical evaluationof ladle slags at voestalpine Stahl GmbH

Abstract

A large number of steel grades are produced at voestalpine Stahl GmbH. The ladle slag must meet different requirements according to the specific steel grade. The mineralogical structure of ladle slag is highly dependent on its basicity. At a basicity of <0·8, spinels occur, and, at higher values, periclase or (Mg,Fe)-wüstite occurs, depending on the degree of slag deoxidation. At basicities between 0·6 and 1·6, calcium aluminates C₁₂A₁₇ and C₃A (C=CaO; A=Al₂O₃) are predominant. Calcium silicates C₂S and C₃S (S=SiO₂) occur throughout the basicity range, and CaO _free occurs at basicities >1·2, both depending on the SiO content. This enables the metallurgist to specifically adjust the ladle slag according to the steel grade requirements. Knowledge of the slag condition is essential in order to achieve certain metallurgical results, such as desulphurisation or degree of oxide purity.