Spheroidizing treatment method for molten metal of spheroidal graphite cast iron

Abstract

A graphite spheroidizing agent containing: 30-80 wt % of Si; Mg; RE (rare earth element) which comprises Ce with a purity level of 80-100 wt % or La with a purity level of 80-100 wt %; Ca; and Al is used. The graphite spheroidizing agent is added so as to satisfy the conditions that an amount of RE equivalent to 0.001-0.009 wt % of the total weight of the molten metal, an amount of Ca equivalent to 0.001-0.02 wt % of the total weight of the molten metal, and an amount of Al equivalent to 0.001-0.02 wt % of the total weight of the molten metal are added to the molten metal, and that the molten metal contains 0.03-0.07 wt % of Mg after the graphite spheroidizing treatment. It is possible to suppress crystallization of chunky graphite in a thick section of spheroidal graphite cast iron and deterioration of mechanical properties, with a low cost.

1 . A spheroidizing treatment method for spheroidizing graphite by addition of a graphite spheroidizing agent to a molten metal, wherein:
 the graphite spheroidizing agent contains: 30-80 wt % of Si; Mg; RE (rare earth element) which comprises Ce with a purity level of 80-100 wt % or La with a purity level of 80-100 wt %; Ca; and Al; and   the graphite spheroidizing agent is added so as to satisfy the conditions that an amount of RE equivalent to 0.001-0.009 wt % of the total weight of the molten metal, an amount of Ca equivalent to 0.001-0.02 wt % of the total weight of the molten metal, and an amount of Al equivalent to 0.001-0.02 wt % of the total weight of the molten metal are added to the molten metal, and that the molten metal contains 0.03-0.07 wt % of Mg after the graphite spheroidizing treatment.   
     
     
         2 . The spheroidizing treatment method according to  claim 1 , wherein the graphite spheroidizing agent further contains S, and the graphite spheroidizing agent is added such that an amount of RE equivalent to 0.002-0.008 wt % of the total weight of the molten metal is added, and a ratio of the amount of RE added to the molten metal to an amount of S added to the molten metal is within a range of 0.06-1.60. 
     
     
         3 . The spheroidizing treatment method according to  claim 1 , wherein the graphite spheroidizing agent contains: 30-80 wt % of Si; 3-8 wt % of Mg; 0.1-0.6 wt % of RE which comprises Ce with a purity level of 80-100 wt % or La with a purity level of 80-100 wt %; 0.1-1.3 wt % of Ca; and 0.1-2.0 wt % of Al, and wherein the graphite spheroidizing agent is added to the molten metal by a sandwich method. 
     
     
         4 . The spheroidizing treatment method according to  claim 1 , wherein the graphite spheroidizing agent contains: 30-80 wt % of Si; 9-25 wt % of Mg; 0.3-1.8 wt % of RE which comprises Ce with a purity level of 80-100 wt % or La with a purity level of 80-100 wt %; 0.1-6.0 wt % of Ca; and 0.1-6.0 wt % of Al, and wherein the graphite spheroidizing agent is added to the molten metal by a wire feeder method. 
     
     
         5 . The spheroidizing treatment method according to  claim 3 , wherein the graphite spheroidizing agent has a particulate shape having a particle diameter of 1-5 mm. 
     
     
         6 . The spheroidizing treatment method according to  claim 3 , wherein the graphite spheroidizing agent has a lumpy shape having a length of 5-70 mm. 
     
     
         7 . The spheroidizing treatment method according to  claim 4 , wherein the graphite spheroidizing agent has a wire-like shape in which graphite spheroidizing agent particles having a particle diameter of 0.1-1.0 mm are included continuously. 
     
     
         8 . The spheroidizing treatment method according to  claim 1 , wherein the spheroidizing treatment is conducted at a temperature of 1400-1500° C., and the molten metal is poured into a mold at a temperature of 1270-1370° C. 
     
     
         9 . The spheroidizing treatment method according to  claim 2 , wherein the graphite spheroidizing agent contains: 30-80 wt % of Si; 3-8 wt % of Mg; 0.1-0.6 wt % of RE which comprises Ce with a purity level of 80-100 wt % or La with a purity level of 80-100 wt %; 0.1-1.3 wt % of Ca; and 0.1-2.0 wt % of Al, and wherein the graphite spheroidizing agent is added to the molten metal by a sandwich method. 
     
     
         10 . The spheroidizing treatment method according to  claim 2 , wherein the graphite spheroidizing agent contains: 30-80 wt % of Si; 9-25 wt % of Mg; 0.3-1.8 wt % of RE which comprises Ce with a purity level of 80-100 wt % or La with a purity level of 80-100 wt %; 0.1-6.0 wt % of Ca; and 0.1-6.0 wt % of Al, and wherein the graphite spheroidizing agent is added to the molten metal by a wire feeder method. 
     
     
         11 . The spheroidizing treatment method according to  claim 9 , wherein the graphite spheroidizing agent has a particulate shape having a particle diameter of 1-5 mm. 
     
     
         12 . The spheroidizing treatment method according to  claim 9 , wherein the graphite spheroidizing agent has a lumpy shape having a length of 5-70 mm. 
     
     
         13 . The spheroidizing treatment method according to  claim 10 , wherein the graphite spheroidizing agent has a wire-like shape in which graphite spheroidizing agent particles having a particle diameter of 0.1-1.0 mm are included continuously. 
     
     
         14 . The spheroidizing treatment method according to  claim 2 , wherein the spheroidizing treatment is conducted at a temperature of 1400-1500° C., and the molten metal is poured into a mold at a temperature of 1270-1370° C.