Nodular graphite cast iron with high strength and high toughness

Abstract

A nodular graphite cast iron is provided, having a pearlite matrix, with high strength and high toughness. The nodular graphite cast iron consists essentially of, by weight %,: from 3.0 to 4.6% of carbon; from 1.6 to 2.5% of silicon; from 0.2 to 0.6% of manganese; from 0.02 to 0.05% of magnesium; from 0.0004 to 0.090% of zirconium; at least one of tin and copper such that α ranges from 0.01 to 0.06% where α indicates a tin conversion amount defined by a summation of a weight % of the tin and 0.1×a weight % of the copper; and the balance of iron and inevitable foreign matters.

What is claimed is:  
     
         1 . A nodular graphite cast iron consisting essentially of: 
 from 3.0 to 4.6 weight % of carbon;    from 1.6 to 2.5 weight % of silicon;    from 0.2 to 0.6 weight % of manganese;    from 0.02 to 0.05 weight % of magnesium;    from 0.0004 to 0.090 weight % of zirconium;    at least one of tin and copper such that the sum of a weight % of the tin and 0.1 times a weight % of the copper ranges from 0.01 to 0.06 weight %; and    a balance of iron and inevitable impurities.    
     
     
         2 . The nodular graphite cast iron according to  claim 1 , wherein the carbon is from 3.1 to 4.5 weight %.  
     
     
         3 . The nodular graphite cast iron according to  claim 1 , wherein the silicon is from 1.7 to 2.4 weight %.  
     
     
         4 . The nodular graphite cast iron according to  claim 1 , wherein the manganese is from 0.3 to 0.5 weight %.  
     
     
         5 . The nodular graphite cast iron according to  claim 1 , wherein the magnesium is from 0.03 to 0.05 weight %.  
     
     
         6 . The nodular graphite cast iron according to  claim 1 , wherein the zirconium is from 0.0005 to 0.080 weight %.  
     
     
         7 . The nodular graphite cast iron according to  claim 1 , wherein the nodular graphite cast iron is a non-heat-treated nodular graphite cast iron.  
     
     
         8 . The nodular graphite cast iron according to  claim 1  wherein the nodular graphite cast iron has a tensile strength of 700 MPa or more and an impact value of 15 J/cm 2  or more.  
     
     
         9 . A method of making a nodular graphite cast iron, the method comprising 
 heating a melt containing carbon, silicon, manganese, magnesium, zirconium, iron and at least one of tin and copper; and producing the cast iron of  claim 1.