Dephosphorization Kinetics and Reaction Region in Hot Metal during Lime Injection with Oxygen

Abstract

To improve dephosphorization of hot metal by the lime injection process, it is necessary to clarify the dissolution mechanism of blown-in CaO in hot metal, the mechanism o f dephosphorization reaction and the region where the reaction takes place. For this purpose, a single-crystal lime lump immersion test and a lime powder injection test were made. Lime lumps after immersion tests, reaction products adhered to Al₂O₃ tubes immersed into hot metal and collected slag samples by steel samples were analyzed by EPMA.
In hot metal, CaO starts to dissolve due to penetration o f Fe_tO and Mn_tO. Then, the dephosphorization reaction initiates between {CaO-Fe (Mn)_tO}l and phosphorus, and the latter is fixed as (CaO-SiO₂ P₂O₅)_s in the reaction layers. Dephosphorization takes place mainly in the vicinity of the oxygen blowing nozzle.
The slagging rate of solid CaO decreases with increasing distance between the nozzle and the suspending position of CaO since carbon in hot metal consumes oxygen. The dephosphorization rate also decreases with increasing distance since Fe_tO in {CaO-Fe (Mn)_tO}l is reduced by carbon.
It is concluded that the increases both in the slagging rate of solid lime and oxygen potential in the bath is necessary to enhance the dephosphorization rate and in this sense, the injection of iron oxide with oxygen is effective.