Mechanism study on formation and chemical changes of calcium aluminate inclusions containing SiO₂ in ladle treatment of tool steel

Abstract

The formation and chemical changes of non-metallic inclusions in the ladle treatment were studied with laboratory experiments and theoretical analysis. Refractory samples covered by the ladle glaze were taken from used ladle and examined. The detachment of ladle glaze and the chemical transformations of oxide solution in the MgO matrix were investigated. After 120 min of reaction with liquid steel, the infiltrated layer of ladle glaze still remained on the surface of refractory samples. This observation showed evidently that the ladle glaze could be the source of inclusions continually during the ladle treatment. The results also explained why the infiltrated liquid oxide could supply inclusion to the steel after two heats. Samples of liquid oxide solution to simulate the liquid oxide inclusions carried over from electric arc furnace (EAF) were equilibrated with liquid steel under controlled atmosphere. The experimental results along with thermodynamic calculation suggested that the SiO₂ content of inclusions carried over from the EAF could be considerably reduced by dissolved aluminium in the steel. This would explain the vanishing of the liquid inclusions containing 30 mass-%SiO₂ after deoxidation in ladle treatment.

Keywords:

• Non-metallic inclusion
• Ladle treatment
• Ladle glaze
• Tool steel

The authors are thankful to the researchers at the chemical analysis laboratory of Uddeholm Tooling AB for their valuable help throughout this study. Financial supports for this work provided by Uddeholm Tooling AB, Hagfors, Sweden are gratefully acknowledged.