| 摘要 |
PROBLEM TO BE SOLVED: To carryout dephosphorizing treatment without causing foaming by blowing a dephosphorizing agent together with gaseous oxygen into molten iron through a lance while adjusting the basicity of top slag on the molten iron held in a vessel to in a specified range. SOLUTION: The basicity of the top slag is adjusted to 1.5-3.0 and the top slag 9 is formed on the molten iron 3 in a torpedo car 1. The dephosphorizing agent is blown together with the gaseous oxygen 6 from the immersion lance 2 to execute the dephosphorization, and the dephosphorizing agent is composed of lime and a oxidizing agent such as iron oxide. When the dephosphorization is executed, the supplying ratio of the dephosphorizing agent and the oxygen and the supplying speed are adjusted so that the basicity in the top slag 9 is adjusted to 1.5-3.0. For preventing the foaming of the top slag 9, the dipping depth 7 of the lance is desirable to be 25-60% of molten iron depth. Desulfurizing treatment is executed to the pretreated molten iron obtd. with the dephosphorizing treatment, and it is suitable to simplify the converter operation and the secondary refining. Further, it is desirable to execute desiliconizing treatment to the molten iron with the treatment of desiliconizing of the casting floor, etc., so as to become <=0.35% Si content.
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