| 摘要 |
PROBLEM TO BE SOLVED: To provide a dephosphorizing method with which phosphorus concentration can be efficiently and surely made a low grade, for preparing extra-low phosphorus steel by melting. SOLUTION: When the dephosphorizing treatment of the molten iron is performed by supplying gaseous oxygen and solid oxygen sources in a top-blown and bottom-blown converter type refining vessel prior to a decarburizing process, the oxygen ratio of the solid oxygen source to the whole oxygen is controlled to 10-60%, and the oxygen quantity to be supplied during treatment, which is the oxygen quantity except for the oxygen to be used for desiliconizing reaction, is controlled to 16-22 Nm<SP>3</SP>/t. Further, grain size of calcined lime to be charged is controlled to 5-40 mm, and the ratio of recessed depth L of the molten iron and the depth L<SB>O</SB>of the bath when the gaseous oxygen is blown is controlled to 0.01-0.20. The bottom-blown stirring power densityεis controlled to 0.5-3.5 kw/t, and the molten iron temperature after the dephosphorizing treatment is controlled to 1,280-1,340°C to perform the dephosphorizing treatment. COPYRIGHT: (C)2011,JPO&INPIT |
