Effect of vacuum degassing on non-metallic inclusions in an ASEA-SKF ladle furnace

Abstract

The objective of this research was to study non-metallic inclusions during vacuum degassing in an ASEA-SKF ladle furnace. Five steel and top slag samples were taken before, during and after vacuum degassing for chemical analysis and scanning electron microscopy. It was concluded that the average CaO/Al₂O₃ ratios in the top slags became close to the phase C₃A. The average CaO/Al₂O₃ ratios in the inclusions of this study were close to the phase CA₆, but at the end of degassing, the average CaO/Al₂O₃ ratios in the calcium aluminates by subtracting the Al amounts of the inclusions that were assumed to form spinel phases with the available Mg amounts in the inclusions were situated between the phases C₁₂A₇ and C₃A. By decreasing the S and Al contents of molten steel and at [S]³.[Al]² less than around 10⁻⁷ , the ratio of calcium aluminates to spinels increased continously. It was finally concluded that by increasing the Ca amount in inclusions, their equivalent circle diameters grew, and their aspect ratios went toward unity, and when the amount of Ca measured in the inclusions was more than ∼25 wt-%, inclusions with bigger equivalent circle diameters appeared.