Influence of Temperature on Dephosphorization at Lower Basicity and Lower Temperature Based on Industrial Experiments and IMCT

Abstract

In the present work, the dephosphorization experiments by using new double slag converter steelmaking process (NDSP) has been carried out in a 180 ton top-bottom combined blowing converter under the low temperature range of 1345–1450°C and low basicity of about 1.50. With increasing dephosphorization endpoint temperature, the dephosphorization ratio, the P₂O₅ content and phosphorus distribution ratio logL_P first increase and then decrease. The apparent equilibrium constant of dephosphorization reaction first increases and then decreases, and the viscosity of dephosphorization slag decreases. The average area fraction of the P-rich phase first increases and then decreases, and those of the matrix phase and the Fe-rich phase increase and decrease, respectively. The morphologies of P-rich phase change from small oval shapes to long strips, then to massive shape, and further to irregular small blocks. The value of the coefficient n in nC₂S–C₃P of P-rich phase first decreases from 4.8–6 to 2–4.8, then increases to 6–20. Based on ion-molecule coexistence theory (IMCT), C₂S and C₃P have the strongest affinities in the calcium silicate and calcium phosphate in the dephosphorization slag, respectively. Increasing the enrichment degree of C₂S–C₃P in the dephosphorization slag is conducive to improving the phosphorus enrichment capacity of the dephosphorization slag and dephosphorization ratio of hot metal. The changing trends of phosphorus enrichment degree in dephosphorization slag characterized by the measurement results of slag phases and the calculation results of IMCT are well consistent, indicating that the IMCT calculation results can correctly express the phosphorus enrichment degree of dephosphorization slag.