Charakterisierung von Schlackenphasen und deren Auswirkung auf den LD-Prozess

To achieve the required target phosphorus content in BOF steel, the binding of phosphorus in the forming mineralogical phases of BOF slag and the resulting slag viscosity are crucial. In order to investigate the impact of fluctuating raw material qualities and the significantly increased initial phosphorus content in pig iron (up to 1200 ppm) on the phase formation and the potential phosphorus absorption capacity of the slag, the mineralogical composition of operational slags with a deliberately set P‑start content of 1200 ppm was determined using analytical methods, such as LOM, SEM-BSE/EDX, XRF, and XRD. This was compared to the composition of reference slags (P-start content < 25 ppm), which was also analyzed. Furthermore, to assess the plausibility and future applicability of thermodynamically obtained results, a comparison was made between the experimentally identified phase composition and that derived from thermodynamic calculations using the FactSage 8.1 software. It was found that the continuous presence of β‑dicalcium silicate (larnite) in the high‑P slags, which serves as the primary phase for dephosphorization, resulted in phosphorus incorporation in this phase across all methods. However, both analytically and thermodynamically, it was evident that this phase, along with other primary phases in the slag, exists as a solid phase. Consequently, at high P levels, the slag viscosity, a crucial factor influencing the progress of metallurgical reactions in the BOF converter, is significantly affected. This limits the optimization potential in terms of controlling phase formation through adjustments to additions.