Experiments on hot metal dephosphorization by using the mixtures of Fe-oxide and Mn-oxide as oxidant were achieved by the use of Tammann furnace. The results were analyzed by the coupled reaction model which consisted of mass transfer equations of each component. Among many unknown parameters in the model, the effective equilibrium constants of P, Mn and S and the mass transfer coefficient in slag phase were changed by the experimental condition and determined by fitting to the experimental result. The observed distribution ratio of P, S and Mn was consistent with the calculated value for each experiment and the applicability of the coupled reaction model was proved. (1) When a mixture of Fe-oxide and Mn-oxide was used as oxidant, as the ratio of FeO to the total content of Fe-oxide and Mn-oxide in flux decreased, the effective equilibrium constants of P and S and the mass transfer coefficient in slag decreased and the effective equilibrium constant of Mn increased. This result indicated that the degree of dephosphorization, desulfurization, Mn recovery and the reaction rate of these reactions increased as the increase of Fe-oxide ratio in flux. (2) The addition of CaF2 and CaCl2 did not significantly change the effective equilibrium constants but modified the mass transfer coefficient in slag. Together with the result of temperature dependence, the necessary amount of CaF2 to obtain the equivalent reaction rate for each temperature was clarified. (3) The activity coefficients of FeO, P205 and MnO converted from the effective equilibrium constants were compared with those values calculated by the thermodynamic models. However satisfactory agreements were not obtained especially for TMno.

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Sy nopsis S)lfllhetic slags wilh low FeO content were produced by way of trial with a view to purifying liquid steel by p reventing its reoxidation by the slag in the ladle. Using the J-ton E.F., low-carbon aluminium-killed steel was tested on a semi-industrial scale. The e.fJects of slags and lining materials by types were investigated, and the following results were obtained: (1) If the F eO content in slag in the ladle is decreased to less than 2 % , liquid steel is /JUrijied and the total oxygen decreases to below 40 NJln. Lmge inclusions (;:;; 100 I') are eliminated. (2) Loss of so l. A I in liquid steel is caused not only by slag but also by lining material. En the case of treatment with synthetic slag, relative contribution of lining material to the loss of so l. A I is greater than in the case of treatment with normal slag. H owever, lhis contribution can be suppressed by the use of a lining material with high A I 2 0 a conlenl. (3) The velocity of so l. A I loss is controlled by the diffusion of oxygen in the slag.

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