Synopsis 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 A1203 tubes immersed into hot metal and collected slag samples by steel

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... les were analyzed by EPMA. In hot metal, CaO starts to dissolve due to penetration o f FetO and Mn1O. Then, the dephosphorization reaction initiates between {CaO-Fe (Mn)rO}t and phosphorus, and the latter is fixed as (CaO-Si02 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 Fe1O in {CaO-Fe (Mn)t0}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. In view of the above-mentioned statement, an alumina tube and a sampler (see Fig. 2 ) were firstly immersed into hot metal, through which lime powder was injected with oxygen, and the floating reaction product was allowed to adhere to the tube or enter the sampler in order to examine the reaction process of CaO. Then, a single-crystal lime lump was immersed into hot metal melted in a crucible and oxygen was injected to examine the slagging process of CaO and the mechanism of dephosphorization. The reason why a lime crystal is used is that a single crystal is suitable to observe the reaction layer without the effect of voids and grainboundaries. Further, alumina tubes, steel samplers and single-crystal lime lumps were immersed into hot metal at various positions in order to know the region where the injected lime reacts. The dephosphorization mechanism of hot metal and the region where dephosphorization takes place during lime injection with oxygen were discussed on the basis of the results of these experiments. I. Introduction Lately, the dephosphorization process of hot metal by injection of mixed flux of lime and iron oxide has been developed and adapted in commercial operation, and lime injection with oxygen is also tested at some plants. The slagging rate of CaO has a great effect on the slag-metal reaction in the steel making process. For this reason, many fundamental and practical studies'-'o~ have so far been made on the mechanism of CaO dissolution into slag and the dissolution rate. In hot metal dephosphorization by lime injection, however, it is not always clear how the injected lime forms slag in hot metal and reacts with phosphorus. In this respect, Haida et al.,"~ have recently discussed the mechanism of dephosphorization by CaO. Fe1O from the results of hot metal dephosphorization by