Effects of calcium ferrite slag on dephosphorization of hot metal during pretreatment in the BOF converter

A study was carried out to examine effects of calcium ferrite slag on dephosphorization of hot metal in the steelmaking BOF, with aims to pick up the speed of slag-forming, increase the slag dumping rate. Laboratory tests using a resistance furnace were performed to examine melting characteristics of calcium ferrite pellets, designed with the optimum ratio of iron oxides (total Fe 55%) to CaO of 3:1. The pellets were put in crucibles with furnace temperature held in the range of 1250-1350 degrees C for 10 min. The results showed that the melting of pellets was nearly completed at 1250 degrees C and main mineral phases, detected by XRD, in the melted samples were CaO center dot Fe2O3 and 2CaO center dot Fe2O3 . Based on results of the laboratory tests, experiments of full scale were performed using a converter of 120t, charging the hot metal with C 3.46-6.81%, Si 0.1-1.16%, Mn 0.12-0.30%, P 0.10-0.18%, S 0.017-0.13% and temperature of 1234-1430 degrees C. For the 13 test heats with 6 min of oxygen blowing, the rate of dephosphorization and phosphorus distribution ratio reached to 50-60% and 55.9, respectively, when the calcium ferrite pellets were charged. Averaged slag basicity 1.5-2.0, slag melting point 1280-1310 degrees, slag viscosity 0.5 pa.s were obtained for the BOF heats adding the calcium ferrite pellet, which ensured the slag foaming height controlled at 2.5-3.0 m during the early stages of the blow. Using above smelting process has increased the rate of slag dumping controlled at 50-70% and enhanced the rate of hot metal dephosphorization over 90%. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).