Method for denitrifying molten steel

Abstract

Proposed is a technology capable of inexpensively and stably reducing the nitrogen concentration in molten steel within a melting furnace or a refining furnace to a low nitrogen concentration range. Provided is a method for denitrifying molten steel including supplying an oxygen-containing gas and a carbon source carried with a carrier gas to the molten steel charged into a melting furnace or a refining furnace, in which the oxygen-containing gas and the carbon source are simultaneously blown onto the molten steel under a condition that, provided that a triangle ΔXYZ is defined by connecting, in a plan view seen from above, a distal end (point X) of a discharge port of a carbon-source blowpipe; an intersection point (point Y) between an inner wall of the furnace and a line obtained by extending a central axis of a carbon source blowing direction; and a distal end (point Z) of a discharge port of an oxygen-blowing lance, that a pointW is positioned on a side XY that is away from the point X by a distance ⅔ a length of the side XY, and that an angle) θ1(°) is an angle ∠XZW, an angle θ2(°) of an oxygen-containing-gas blowing direction that is open toward a Y side with respect to a side ZX passing through the distal end (point Z) of the discharge port of the oxygen-blowing lance in the plan view seen from above is a positive value and is the angle θ1 or less.

1 . A method for denitrifying molten steel comprising supplying an oxygen-containing gas and a carbon source carried with a carrier gas to the molten steel charged into a melting furnace or a refining furnace,
 wherein   the oxygen-containing gas and the carbon source are simultaneously blown onto the molten steel under a condition that, provided that a triangle ΔXYZ is defined by connecting, in a plan view seen from above, a distal end (point X) of a discharge port of a carbon-source blowpipe; an intersection point (point Y) between an inner wall of the furnace and a line obtained by extending a central axis of a carbon source blowing direction; and a distal end (point Z) of a discharge port of an oxygen-blowing lance, that a point W is positioned on a side XY that is away from the point X by a distance ⅔ a length of the side XY, and that an angle) θ 1 (°) is an angle ∠XZW, an angle θ 2 (°) of an oxygen-containing-gas blowing direction that is open toward a Y side with respect to a side ZX passing through the distal end (point Z) of the discharge port of the oxygen-blowing lance in the plan view seen from above is a positive value and is the angle θ 1  or less.   
     
     
         2 . The method for denitrifying molten steel according to  claim 1 , wherein
 when the carbon-source blowpipe includes a plurality of carbon-source blowpipes, the condition is satisfied in relation to at least one of the carbon-source blowpipes.   
     
     
         3 . The method for denitrifying molten steel according to  claim 1 , wherein
 a time t 1  (min) for simultaneously supplying the carbon source and the oxygen-containing gas from the carbon-source blowpipe and the oxygen-blowing lance, respectively, is set to at least 30% or more of a time t 2  (min) taken from a start of melting a cold iron source to a start of tapping the molten steel from the furnace.   
     
     
         4 . The method for denitrifying molten steel according to  claim 2 , wherein
 a time t 1  (min) for simultaneously supplying the carbon source and the oxygen-containing gas from the carbon-source blowpipe and the oxygen-blowing lance, respectively, is set to at least 30% or more of a time t 2  (min) taken from a start of melting a cold iron source to a start of tapping the molten steel from the furnace.   
     
     
         5 . The method for denitrifying molten steel according to  claim 1 , wherein
 the point W is positioned at a middle point of the side XY.   
     
     
         6 . The method for denitrifying molten steel according to  claim 1 , wherein
 the melting furnace is an electric furnace.   
     
     
         7 . The method for denitrifying molten steel according to  claim 5 , wherein
 the melting furnace is an electric furnace.   
     
     
         8 . The method for denitrifying molten steel according to  claim 2 , wherein the point W is positioned at a middle point of the side XY. 
     
     
         9 . The method for denitrifying molten steel according to  claim 3 , wherein the point W is positioned at a middle point of the side XY. 
     
     
         10 . The method for denitrifying molten steel according to  claim 4 , wherein the point W is positioned at a middle point of the side XY. 
     
     
         11 . The method for denitrifying molten steel according to  claim 2 , wherein the melting furnace is an electric furnace. 
     
     
         12 . The method for denitrifying molten steel according to  claim 3 , wherein the melting furnace is an electric furnace. 
     
     
         13 . The method for denitrifying molten steel according to  claim 4 , wherein the melting furnace is an electric furnace. 
     
     
         14 . The method for denitrifying molten steel according to  claim 8 , wherein the melting furnace is an electric furnace. 
     
     
         15 . The method for denitrifying molten steel according to  claim 9 , wherein the melting furnace is an electric furnace. 
     
     
         16 . The method for denitrifying molten steel according to  claim 10 , wherein
 the melting furnace is an electric furnace.