| The dephosphorization by double-deslagging operation in 120t top-bottom combined blown converter steelmaking process by Factsage 6.4 software, XRD, SEM-EDS,Raman spectral spectroscopy and Fourier transformation infrared (FTIR) analysis. The study includes converter dephosphorization, process control of first deslagging, process control of end point and the effect of slag thermophysical properties on dephosphorization.To achieve relatively efficient dephosphorization in 120t combined blown converter, scrap ratio should be in the range of 10%-12%, the temperature of the hot metal into is 1300℃ or more. It is favourable for dephosphorization at initial stage and attaining the dephosphorization ratio large than 92% when auxiliary materials of once addition ratio is controlled between 65% and 70%. Oxygen supply intensity is greater than 3.10 m3/(min·t). The double-deslagging operation and double-deslagging combining with remaining slag were compared. The advantageous condition of double-deslagging combining with remaining slag for dephosphorization was clarified.It was proposed that the liquid steel temperature at the equilibrium of [C]-(FeO)-[P] should be used as the temperature for starting first deslagging. This criteria was applied in practical converter dephosphorization, and contributes to an increase of dephosphorization ratio 28% compared with the criteria using carbon and phosphorus selective oxidation temperature as the control temperature. Production experiment shows that, first deslagging has the decarburization reaction in liquid steel. When carbon content is greater than 3.2%, phosphorus content of liquid steel in first deslagging decreases with decreasing carbon content. When the liquid temperature of first deslagging between1390℃～1425℃, slag basicity is greater than 2.0, content of (FeO%) above 10.0%, (MgO%) and arrange in 5.8%～6.5% and 6～8 respectively, dephosphorization rate of first deslagging will achieve above 65%.The effects of interaction of terminal carbon, oxygen, temperature and the after-stirring process on the dephosphorization were studied. With the increase of terminal temperature, the phosphorus content in the steel increased. When the tapping terminal temperature of high carbon steel is controlled between 1620℃ to 1640℃,phosphorus content in liquid steel can be reduced less than 0.0080%.If the tapping terminal temperature of low carbon steel was controlled between 1620℃ to 1640℃, phosphorus content in liquid steel can be reduced less than 0.0050%. The method of improving the slag basicity and oxidation can be adopted to reduce the adverse effects on the dephosphorization caused by the high tapping temperature. In addition, the reasonable control of the slag basicity and composition, and application of phosphorus content are beneficial to reach the equilibrium between the liquid and slag, and further reduce the phosphorus content in liquid. Finally, the process for controlling the phosphorus content less than 0.005% is proposed.The study on the effect of converter slag on dephosphorization showed that Si, Ca and P in the first deslagging and terminal slag almost enriched in 2CaO·SiO2,3CaO·P2O5 and 2CaO·SiO2-3CaO·P2O5, which is in favorable of dephosphorization. The more of 2CaOSiO2,3CaO·P2O5 and 2CaO·SiO2-3CaO·P2O5 in slag, the more favorable dephosphorization. The lower of the melting point of the converter slag is, the more favorable dephosphorization. The melting point of the converter slag can be adjusted by the alkalinity and the content of FeO and MnO in order to create favorable conditions for dephosphorization. The more of [FeO4]-tetrahedral and Si-O-Si bond in the converter slag structure, the more favorable dephosphorization. Simultaneously, the more Q0 and Q2 in converter slag, the more adverse for dephosphorization. |
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