Method for refining molten iron

Abstract

A method for refining molten iron that can stably produce low-nitrogen steel is proposed. In this method for refining molten iron, untreated molten iron with a carbon concentration [C] i between 0.5 mass % and 3.0 mass %, both inclusive, is placed into a vessel, and oxygen is blown onto the untreated molten iron under atmospheric pressure while a hydrogen gas, a hydrocarbon gas, or a mixture gas of these gases is blown in to perform a decarburization and denitrification treatment of the untreated molten iron. It is preferable, for example, that a nitrogen concentration [N] f in treated molten iron after being subjected to the decarburization and denitrification treatment be 30 mass ppm or lower; that treated molten iron after being subjected to the decarburization and denitrification treatment be further subjected to a vacuum degassing treatment; that the untreated molten iron include molten iron obtained by melting a cold iron source; that the untreated molten iron be a mixture of primary molten iron obtained by melting a cold iron source in a melting furnace and molten pig iron having a carbon concentration of 2.0 mass % or higher; that the cold iron source include reduced iron; and that the vessel be a converter.

1 . A method for refining molten iron, wherein
 untreated molten iron with a carbon concentration [C] i  between 0.5 mass % and 3.0 mass %, both inclusive, is placed into a vessel, and   oxygen is blown onto the untreated molten iron under atmospheric pressure while a hydrogen gas, a hydrocarbon gas, or a mixture gas of these gases is blown in to perform a decarburization and denitrification treatment of the untreated molten iron.   
     
     
         2 . The method for refining molten iron according to  claim 1 , wherein a nitrogen concentration [N] f  in treated molten iron after being subjected to the decarburization and denitrification treatment is 30 mass ppm or lower. 
     
     
         3 . The method for refining molten iron according to  claim 1 , wherein
 treated molten iron after being subjected to the decarburization and denitrification treatment is further subjected to a vacuum degassing treatment.   
     
     
         4 . The method for refining molten iron according to  claim 1 , wherein
 the untreated molten iron includes molten iron obtained by melting a cold iron source.   
     
     
         5 . The method for refining molten iron according to  claim 1 , wherein
 the untreated molten iron is a mixture of primary molten iron obtained by melting a cold iron source in a melting furnace and molten pig iron having a carbon concentration of 2.0 mass % or higher.   
     
     
         6 . The method for refining molten iron according to  claim 4 , wherein
 the cold iron source includes reduced iron.   
     
     
         7 . The method for refining molten iron according to  claim 1 , wherein
 the vessel is a converter.   
     
     
         8 . The method for refining molten iron according to  claim 2 , wherein
 treated molten iron after being subjected to the decarburization and denitrification treatment is further subjected to a vacuum degassing treatment.   
     
     
         9 . The method for refining molten iron according to  claim 2 , wherein
 the untreated molten iron includes molten iron obtained by melting a cold iron source.   
     
     
         10 . The method for refining molten iron according to  claim 3 , wherein
 the untreated molten iron includes molten iron obtained by melting a cold iron source.   
     
     
         11 . The method for refining molten iron according to  claim 8 , wherein
 the untreated molten iron includes molten iron obtained by melting a cold iron source.   
     
     
         12 . The method for refining molten iron according to  claim 2 , wherein
 the untreated molten iron is a mixture of primary molten iron obtained by melting a cold iron source in a melting furnace and molten pig iron having a carbon concentration of 2.0 mass % or higher.   
     
     
         13 . The method for refining molten iron according to  claim 3 , wherein
 the untreated molten iron is a mixture of primary molten iron obtained by melting a cold iron source in a melting furnace and molten pig iron having a carbon concentration of 2.0 mass % or higher.   
     
     
         14 . The method for refining molten iron according to  claim 8 , wherein
 the untreated molten iron is a mixture of primary molten iron obtained by melting a cold iron source in a melting furnace and molten pig iron having a carbon concentration of 2.0 mass % or higher.   
     
     
         15 . The method for refining molten iron according to  claim 5 , wherein
 the cold iron source includes reduced iron.