Research on the mechanism of phosphorus removal in the converter with single slag method

Abstract

For the purpose of make better use of high-phosphorus hot metal to produce low-phosphorus clean steel by single-slag converter smelting, based on industrial test data, the influence of process parameters on dephosphorization efficiency in the process of single-slag converter smelting was systematically studied, and the effects of different hot metal temperature and Si content of hot metal into the converter, different lime tons of steel, temperature and C content of molten steel at the end point, and FeO, MgO, P₂O₅, Al₂O₃ and R (R is the alkalinity of the slag, and R = CaO/SiO₂) in the final slag of the converter were compared. Thus, the influence mechanism of single-slag converter smelting process parameters on dephosphorization was revealed. The combination of X-ray diffraction (XRD) and scanning electron microscope with an energy-dispersive X-ray spectroscopy (SEM-EDS) characterization techniques revealed the mechanism of the final slag facies structure and phosphorus occurrence morphology. The analysis reveals that: when the temperature of the hot metal entering the converter is ≥1320 °C and w(Si) < 0.15%, the controlling lime addition amount is 18–21 kg t⁻¹, the end temperature is 1600–1630 °C, the carbon content of the endpoint is equal to or less than 0.06%, and the composition of the end slag phase is w(FeO) = 19%–26%, w(MgO) ≤ 8.0%, w(P₂O₅) ≤ 3.6%, and w(Al₂O₃) ≤ 1.8%, and the high-efficiency dephosphorization can be achieved. Mineral facies analysis showed that the dephosphorization products mainly existed in the form of Ca₁₅(PO₄)₂(SiO₄)₆ of Nagistmitite, which was verified by XRD phase identification and SEM-EDS micro-component analysis, and its morphological characteristics showed the edge diffuse distribution of RO phase (FeO-MnO-MgO solid solution). This study clarifies the influencing mechanism of dephosphorization of single-slag converter and provides a practical reference for the production of Low Phosphorus Clean Steel by converter low-cost and high-efficiency dephosphorization smelting process.