Method for removing impurities in molten cast iron, and cast iron raw material

Abstract

There is provided a method for obtaining a pure melt in which the impurities Mn, Al, Ti, Pb, Zn, and B are removed from molten cast iron and depletion of useful C and Si is suppressed, the method wherein an excess oxygen flame having a theoretical combustion ratio of fuel and oxygen (amount of oxygen (volume)×5/amount of fuel (volume)) of 1 to 1.5 is directly exposed to the surface of pre-melted molten cast iron, the temperature of the molten cast iron is held at 1250° C. or more and less than 1500° C. while the melt surface is superheated and an acidic slag is brought into contact with the melt, and an oxygen-containing gas is injected into the interior of the molten cast iron.

1 . A method for removing impurities including manganese (Mn) while suppressing the depletion of carbon (C) and silicon (Si) included in pre-melted molten cast iron, the method for removing impurities in molten cast iron characterized in comprising: holding the temperature of the molten cast iron at 1250° C. or more and less than 1500° C.; and directly exposing a surface of the molten cast iron to an excess oxygen flame having a theoretical combustion ratio of fuel and oxygen (amount of oxygen (volume)×5/amount of fuel (volume)) of 1 to 1.5 while allowing the melt and an acidic slag layer to come into contact with each other to superheat the surface. 
     
     
         2 . The method for removing impurities in molten cast iron of  claim 1 , characterized in being a method in which (ΔC/ΔMn) or (ΔSi/ΔMn) is 2.5 or less when the removal efficiency per unit time of the manganese (Mn) is (ΔMn/h), the removal efficiency per unit time of the carbon (C) is (ΔC/h), and the removal efficiency per unit time of the silicon (Si) is (ΔSi/h). 
     
     
         3 . The method for removing impurities in molten cast iron of  claim 1  or  2 , characterized in that an oxygen-containing gas is injected from the interior of the molten cast iron to a surface of the molten cast iron on which the excess oxygen flame is directly exposed. 
     
     
         4 . The method for removing impurities in molten cast iron of  claim 3 , characterized in that the oxygen-containing gas is air. 
     
     
         5 . The method for removing impurities in molten cast iron of  claim 3  or  4 , characterized in that the oxygen-containing gas is injected at 100 to 1600 (L/min) per 1000 kg of melt. 
     
     
         6 . The method for removing impurities in molten cast iron of any of  claims 1  to  5 , characterized in that elements other than manganese (Mn) removed as impurities in the molten cast iron are at least one of the elements selected from lead (Pb), zinc (Zn), titanium (Ti), aluminum (Al), and boron (B). 
     
     
         7 . The method for removing impurities in molten cast iron of any of  claims 1  to  6 , characterized in that iron oxide is added to the molten cast iron. 
     
     
         8 . The method for removing impurities in molten cast iron of any of  claims 1  to  7 , characterized in that a device for holding the molten cast iron is a rotary furnace, an electric furnace, a ladle, a cupola desulfurization ladle, or a turn dish, or a combination thereof. 
     
     
         9 . A cast iron raw material manufactured using the method of  claim 1 , the cast iron raw material characterized in being 2 to 4 mass % carbon (C), 0.5 to 4 mass % silicon (Si), 0.1 to 3 mass % manganese (Mn), 0.0001 to 0.03 mass % lead (Pb), 0.0001 to 1.0 mass % zinc (Zn), 0.001 to 0.2 mass % titanium (Ti), 0.0001 to 0.5 mass % aluminum (Al), 0.0001 to 0.04 mass % boron (B), and the remainder being iron (Fe) and inevitable impurities.