| 摘要 |
PROBLEM TO BE SOLVED: To produce molten steel with good productivity by controlling the amt. of the bottom blowing gas to a specified amt. at the time of steel making and refining by decarburization by subjecting molten iron to prerefining of desiliconizing and dephosphorizing in a converter having bottom blown tuyeres, then discharging molten slag. SOLUTION: The molten iron is put into the converter having the bottom blowing tuyeres. The oxidizing gaseous CO2 is blown from the bottom tuyeres to oxide the Si and P in the molten iron with the CO2 and to slag off both as SiO2 and P2 O5 in the basic molten slag consisting essentially of CaO, etc. After the molten iron is subjected to the predesiliconizing and dephosphorizing refining in such a manner, the molten slag contg. the SiO2 and P2 O5 is discharged from the converter and, in succession, the molten iron is decarburized and refined to the molten steel by oxygen blowing. The amt. of the bottom blowing gas at the time of the predesiliconizing and dephosphorizing refining is controlled in such a manner that the max. value from the min. 40Nm<3> /hour per 1 ton of the molten slag attains the equation: the amt. of the slag in the converter (t/t molten iron)×the flow rate of the bottom blowing gas (Nm<3> /hour/t-molten slag)<=6.0, by which the slopping of the molten slag subjected to the dephosphorization is prevented. The molten iron is thus prerefined with the excellent productivity by completely discharging the molten slag subjected to the dephosphorization.
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