Method for increasing the quality of graphite balls

Abstract

The invention provides a method for increasing the quality of graphite balls. The method comprises melting molten iron in an electric furnace, increasing the sulfur content in the molten iron during the melting process, and adding rare earth in the electric furnace or in a nodularizing ladle; after the molten iron is completely melted, pouring the molten iron into the nodularizing ladle and nodularizing; and after nodularization, adding ferromanganese to a transfer ladle. In the present invention, sulfur is added to molten iron in advance, and rare earth is added to a nodularizing ladle previously, so that a large number of dispersed rare earth sulfide particles are formed in the molten iron during the nodularization process. Rare earth sulfide particles serve as the nuclei of graphite crystallization to increase the number of graphite balls, and improve the roundness of graphite balls.

What is claimed is: 
     
         1 . A method for increasing the quality of graphite balls, comprising steps of: increasing the sulfur content in base molten iron, and adding rare earth to a nodularizing unit, so that dispersed rare earth sulfide particles are formed during a nodularization process, wherein the rare earth sulfide particles serve as the nuclei of graphite crystallization to increase the number of graphite balls, and improve the roundness of graphite balls. 
     
     
         2 . The method according to  claim 1 , wherein the rare earth is selected from the group consisting of cerium, a lanthanum-cerium alloy and a cerium-iron alloy and any combination thereof. 
     
     
         3 . The method according to  claim 1 , wherein the sulfur content is increased by adding sulfur or ferric sulfide. 
     
     
         4 . The method according to  claim 1 , wherein the rare earth accounts for 0.01%-0.08% by weight of the base molten iron. 
     
     
         5 . The method according to  claim 1 , wherein the sulfur content in the sulfur-increased molten iron is 0.03-0.07 wt %. 
     
     
         6 . The method according to  claim 1 , wherein the rare earth is added to the nodularizing unit previously, and the molten iron is poured into the nodularizing unit and nodularized, wherein the rare earth covers the surface of a nodularizer. 
     
     
         7 . The method according to  claim 1 , wherein a raw material of the base molten iron is selected from steel scrap and recycled scrap; and the steel scrap is selected from carbon steel and/or alloy steel. 
     
     
         8 . The method according to  claim 7 , wherein the steel scrap accounts for 50-100 wt %, and the recycled scrap accounts for 0-50 wt % in the raw material. 
     
     
         9 . The method according to  claim 1 , further comprising adding ferrosilicon, and a recarburizer to the base molten iron, to give a carbon content of 3.6-4.0 wt % and a silicon content of 1.8-2.1 wt % in the molten iron. 
     
     
         10 . The method according to  claim 1 , further comprising adding ferromanganese to the molten iron after nodularization, and the ferromanganese has a particle size of 5 to 15 mm. 
     
     
         11 . The method according to  claim 10 , wherein the manganese content in the molten iron is 0.4-0.6 wt %.