JPS55107716A - Decarbonation method of molten iron - Google Patents

Abstract

PURPOSE: To suppress the formation of FeO, etc. by mixing inert gas into oxygen gas, blowing the gas to bath surface and forming recessed surfaces at the end period of blowing at the time of refining the molten iron which has beforehand undergone desiliconization, desulfurization and dephosphorization to low-carbon steel by an oxygen top blowing method.

CONSTITUTION: The molten iron tapped from a blast furnace is subjected to preliminary oxidation refining with gas oxygen and iron-oxide-containing raw materials, whereby it is desiliconized while its decarbonization reaction is being suppressed. At the same time, it is desulfurized and dephosphorized by the addition of flux such as CaCl₂. The molten iron having been pre-refined to Si<0.05%, P<0.025%, S<0.020% in this way is decarbonation-refined in an oxygen top blowing converter or the like, whereby low carbon steel is produced. At the time when C is oxidation-decarbonized to 0.10W0.15% at the end period of blowing, 40W80% of inert gas such as Ar is mixed to blowing oxygen and the gas is blown onto the bath surface to form recesses on the bath surface and stir the molten iron. The CO partial pressure in the recesses of the bath surface is lowered and the decarbonization reaction is progressed under the partial pressure suited for the C concentration in the bath, whereby the low-carbon steel may be produced without forming FeO and MnO.

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