To reduce slag quantity discharged to out of the system in a dephosphorizing process, to enable effective utilization of the discharged slag and to prevent the lowering of iron yield by reusing produced low phosphorus iron slag as flux for dephosphorizing after obtaining the low phosphorus iron by using the flux for dephosphorizing to dephosphorize molten iron, and executing the dephosphorization of the other molten iron under condition of the slag basicity at a specific value or lower.
The molten iron, lime, decarburizing furnace slag produced in the decarburizing furnace refining at the second and/or the fourth process and iron oxide base flux are charged into a dephosphorizing furnace 1 to execute the dephosphorization. The obtd. low phosphorus iron is shifted to a decarburizing furnace 2 the second process and lime base flux is charged and the decarburization is executed to obtain a low phosphorus steel. The third process: New molten iron is charged into the dephosphorizing furnace 1 and the low phosphorus iron slag produce at the first process and the flux consisting essentially of a lime base dephosphorizing agent are charged to execute the dephosphrization under condition of the basicity ≤2. The produced slag can be utilized as a roadbed material, etc. The fourth process: The ordinary phosphorus iron obtd. at the previous process is shifted to the decarburizing furnace 2 and decarburized by charging the lime base flux to obtain the ordinary phosphorus steel.
MATSUO TORU
HIGUCHI YOSHIHIKO
