A method for dephosphorization and removal of nitrogen oxides of chromium hold strength of pig iron

摘要

PURPOSE:To subject pig iron containing Cr to dephosphorizing and denitrifying treatments industrially advantageously by bringing the pig iron of =3% Cr-content in contact with the slag containing alkaline earth metal halide, oxide of Li or its carbonate, iron oxide, etc. while maintaining its Si concentration at the specified value or less. CONSTITUTION:While the molten iron of =3% Cr content is being maintained of its Si concentration at =0.2% and is being suppressed of oxidation of the Cr in it, it is put in contact with the following dephosphorizing and denitrifying slag, whereby it is dephosphorized and denitrified. Namely, the slag containing 30-80% of one or more kinds of fluoride or chloride of alkaline earth metals (e.g.; CaF2), 0.4- 30% of one or more kinds of oxide or carbide of Li (e.g.; Li2CO3) and 5-50% of one or more kinds of iron oxide, Ni oxide (e.g.; Fe2O3) is used. The oxidation suppression of Cr of this case is accomplished by the control of the CO partial pressure of the atmosphere or the control of the C concentration in an iron bath. In addition, this contact treatment is done at temperature up to 1,600 deg.C.