Dephosphorization during blowing in a 5 ton bottom blown converter has been studied. The effects of lime size and injection pattern on dephosphorization have also been investigated in a 230 ton Q-BOP. The phosphorus partition suitable for the bottom blown converter has been obtained by the regression analysis of experimental data.
Injection of lime and premelt powder mixtures into the 5 t test Q-BOP has revealed that dephosphorization proceeds largely in the early stage of blowing. This characteristic has been utilized to develop a new and effective dephosphorization pretreatment of hot metal in Q-BOP. This new technique has enabled us to dephosphorize hot metal from ca. 0.14% to 0.010%P with a consumption of 20 kg CaO/tpig and 3 kg CaF2/t-pig within 2 to 4 minutes of oxygen blowing. The ultra-low phosphorus and sulfur steels have been successfully produced by the newly developed technique.
