Method for producing grained iron, and grained iron

Abstract

A method capable of efficiently producing grained iron with a low P concentration includes a first step of melting reduced iron to obtain primary molten iron, a second step of separating the primary molten iron from slag, a third step of subjecting the primary molten iron separated from the slag to dephosphorization to obtain secondary molten iron, and a fourth step of solidifying the secondary molten iron into a grained form to obtain grained iron, in which in the third step, the dephosphorization is performed by supplying an oxygen source and a CaO source to the primary molten iron, and a temperature of the secondary molten iron at the end of the dephosphorization is set to a temperature of the primary molten iron at the start of the dephosphorization or lower.

1 . A method for producing grained iron, comprising:
 a first step of melting reduced iron to obtain primary molten iron;   a second step of separating the primary molten iron from slag;   a third step of subjecting the primary molten iron separated from the slag to dephosphorization to obtain secondary molten iron; and   a fourth step of solidifying the secondary molten iron into a grain form to obtain grained iron,   wherein:
 in the third step, the dephosphorization is performed by supplying an oxygen source and a CaO source to the primary molten iron, and a temperature of the secondary molten iron at the end of the dephosphorization is set to a temperature of the primary molten iron at the start of the dephosphorization or lower. 
   
     
     
         2 . The method for producing grained iron according to  claim 1 , wherein a temperature T f  of the secondary molten iron at the end of the dephosphorization is set higher than a solidifying temperature T m  of the secondary molten iron at the end of the dephosphorization by 20° C. or more. 
     
     
         3 . The method for producing grained iron according to  claim 1 , wherein a composition of the slag at the end of the dephosphorization is set to have a slag basicity in a range of 1.0 to 4.0, wherein the slag basicity is a ratio of a CaO concentration (% CaO) to a SiO 2  concentration (% SiO 2 ) on a mass basis. 
     
     
         4 . The method for producing grained iron according to  claim 1 , wherein
 the fourth step is performed using a grained iron producing apparatus including a granulation device that forms the secondary molten iron into droplets, a water-flow control vessel that is disposed at a position for receiving the droplets and accommodates cooling water, and at least one cooling water pipe that is connected to the water-flow control vessel and supplies cooling water to the water-flow control vessel, and   the water-flow control vessel includes an inclined surface that is inclined such that a horizontal cross-sectional area of the water-flow control vessel becomes narrower in a downward direction, and a discharge port is provided below the inclined surface.   
     
     
         5 . Grained iron produced from reduced iron with a P concentration of 0.050 mass % or more as a raw material,
 wherein
 a P concentration of the grained iron is 0.030 mass % or less, and size grain of the grained iron is in the range of 1 mm to 50 mm inclusive. 
   
     
     
         6 . The method for producing grained iron according to  claim 2 , wherein a composition of the slag at the end of the dephosphorization is set to have a slag basicity in a range of 1.0 to 4.0, wherein the slag basicity is a ratio of a CaO concentration (% CaO) to a SiO 2  concentration (% SiO 2 ) on a mass basis.