Spheroidal Graphite Cast Iron Excellent in Gas Defect Resistance

Abstract

There is provided with spheroidal graphite cast iron having excellent gas defect resistance where gas defects such as pinholes attributable to the free N are small in number and having mechanical characteristics and machinability equal to or greater than the conventional ones. The spheroidal graphite cast iron consists of, in mass ratio, C: 3.3 to 4%; Si: 2 to 3%; P: not more than 0.05%; S: not more than 0.02%; Mn: not more than 0.8%; Cu: not more than 0.8% (0 is not included); Mg: 0.02 to 0.06%; Ti: 0.01 to 0.04%; V: 0.001 to 0.01%; Nb: 0.001 to 0.01%; and N: 0.004 to 0.008%, with the remnant substantially consisting of Fe and an inevitable impurity.

1 - 5 . (canceled) 
     
     
         6 . A spheroidal graphite cast iron excellent in gas defect resistance consisting of, in mass ratio:
 C: 3.3 to 4%;   Si: 2 to 3%;   P: not more than 0.05%;   S: not more than 0.02%;   Mn: not more than 0.8%;   Cu: not more than 0.8% (0 is not included);   Mg: 0.02 to 0.06%;   Ti: 0.01 to 0.04%;   V: 0.001 to 0.01%;   Nb: 0.001 to 0.01%; and   N: 0.004 to 0.008%,   with the remnant substantially consisting of Fe and an inevitable impurity.   
     
     
         7 . The spheroidal graphite cast iron according to  claim 6 ,
 wherein the spheroidal graphite cast iron contains, in mass ratio, 0.015 to 0.045% Ti, V and Nb in total and further, contains Ti, V, Nb and N so as to satisfy the following expression (1):
   0.8≤(0.29Ti+0.27V+0.15Nb)/N≤2.0  (1)
 
   here, the element symbols in the expression (1) represent the contents [mass ratio (%)] of the elements in the spheroidal graphite cast iron.   
     
     
         8 . The spheroidal graphite cast iron according to  claim 6 ,
 wherein the spheroidal graphite cast iron contains, in mass ratio, not less than 0.005% P and not less than 0.005% S.   
     
     
         9 . The spheroidal graphite cast iron according to  claim 6 ,
 wherein the spheroidal graphite cast iron contains, in mass ratio, not less than 0.2% Mn and not less than 0.1% Cu.   
     
     
         10 . The spheroidal graphite cast iron according to  claim 6 ,
 wherein the spheroidal graphite cast iron is not less than 600 MPa in tensile strength and not less than 12% in elongation.   
     
     
         11 . The spheroidal graphite cast iron according to  claim 6 ,
 wherein a gas defect area ratio of the spheroidal graphite cast iron is not more than 11%.   
     
     
         12 . The spheroidal graphite cast iron according to  claim 6 ,
 wherein a tool life improvement rate of the spheroidal graphite cast iron is not less than 1.0 times.