Desiliconization, dephosphorization, and decarburization methods that reuse desiliconized slag

摘要

PROBLEM TO BE SOLVED: To reduce phosphorus of a molten steel while promoting slag formation during decarbonization by using desiliconized slag having low melting point (SiOsource) and preventing erosion of refractory and reduce slag quantity discharging from whole steel making process.SOLUTION: When manufacturing a molten steel having phosphorus concentration of 0.015 mass% or less from a molten iron, the invention includes a first process of desiliconization at basic degree of 0.6 to 1.2 by supplying an oxygen source, a second process for conducting dephosphorization by supplying a CaO source so that the basic degree becomes 1.2 or more, a third process of separating dephosphorized slag and molten steel after dephosphorization treatment and a fourth process for adding desiliconized slag generated the first process before charging and conducting decarbonization with desiliconized slag satisfying "5/XSiOin the desiliconized slag/SiOin whole auxiliary material10/X" and basicity after the treatment of 3.0 to 4.5. X=(%AlO+%TiO)/(%CaO+%SiO+%AlO+%TiO).