Compacted graphite iron brake drum

Abstract

A compacted graphite iron brake component for use in a braking system having a final composition of: 3.0 to about 4.0 percent carbon; 2.15 to about 2.60 percent silicon; 0.40 to about 0.90 manganese; and the balance iron. The brake component having a frictionally engageable portion with a microstructure of compacted graphite disposed in a pearlitic matrix.

What is claimed is:  
     
         1 . A compacted graphite iron brake drum comprising: 
 (a) a base portion; and    (b) a wall defining an interior friction engagement surface adjoining said base portion, said base portion and said friction portion being composed of a material having a final composition comprising: 
 (i) carbon in an amount of about 3.0 to about 4.0 weight percent;  
 (ii) sulfur in an amount of about 0.001 to about 0.020 weight percent;  
 (iii) the balance primarily iron, said base portion and said friction portion having a microstructure of compacted graphite dispersed in a matrix which is greater than 50% pearlitic; and  
 (iv) the matrix having a substantially homogeneous microstructure of compacted graphite flakes dispersed relatively uniformly through the matrix.  
   
     
     
         2 . The compacted graphite iron brake drum of  claim 1  wherein the matrix has greater than 80% Type IV graphite.  
     
     
         3 . The compacted graphite iron brake drum of  claim 1  having from greater than 50 to 65% pearlitic matrix by volume.  
     
     
         4 . The compacted graphite iron brake drum of  claim 1  having from 65 to 85% pearlitic matrix by volume.  
     
     
         5 . The compacted graphite iron brake drum of  claim 1  having from greater than 50% to 65% pearlitic matrix by volume.  
     
     
         6 . The compacted graphite iron brake drum of  claim 1  having carbon in an amount from 3.30-3.70 weight percent.  
     
     
         7 . The compacted graphite iron brake drum of  claim 1  further comprising: 
 (v) silicon in an amount of about 2.15 to about 2.60 weight percent; and  
 (vi) manganese in an amount of about 0.40 to about 0.90 weight percent.  
 
     
     
         8 . A compacted graphite iron brake drum comprising: 
 (a) a base portion; and    (b) a wall depending upon said base portion, said wall defining an interior friction engagement surface wherein said base portion and side wall comprise: 
 (i) carbon in an amount of about 3.0 to about 4.0 by weight percent;  
 (ii) silicon in an amount of about 2.15 to about 2.60 by weight percent;  
 (iii) manganese in an amount of about 0.40 to about 0.90 by weight percent;  
 (iv) sulfur in an amount of about 0.001 to about 0.020 by weight; and  
   wherein said compacted graphite iron alloy has a matrix which is greater than 50% and less than 85% pearlitic by volume with a graphite formation having Type IV graphite being dispersed therein.    
     
     
         9 . The compacted graphite iron brake drum of  claim 8  wherein the graphite formation contains 80% minimum Type IV graphite.  
     
     
         10 . The compacted graphite iron brake drum of  claim 8  comprising from 65 to 70% by volume pearlitic matrix.  
     
     
         11 . The compacted graphite iron brake drum of  claim 8  comprising from 3.30-3.70% by weight carbon.  
     
     
         12 . The compacted graphite iron brake drum of  claim 8  wherein the matrix has a substantially homogenous microstructure of Type IV flakes dispersed relatively uniformly therein.  
     
     
         13 . The compacted graphite iron brake drum of  claim 8  wherein the matrix has a hardness from about 143 to 255.  
     
     
         14 . A method of forming an iron brake drum having a base portion and a wall having the steps of: 
 (a) preparing a melt of a ferrous base metal;    (b) alloying the melt in a suitable pearlite stabilizer to achieve a primarily pearlitic microstructure;    (c) providing alloying elements into the ferrous base metal to produce a compacted graphite structure; and    (d) pouring the melt to cast an article, wherein the wall has a microstructure of Type IV graphite dispersed in the pearlite matrix.    
     
     
         15 . The method according to  claim 14  wherein providing alloying elements is providing alloying elements into the ferrous base metal to produce a matrix of compacted graphite flakes dispersed relatively uniformly through the matrix.  
     
     
         16 . The method according to  claim 14  wherein the compacted graphite structure has greater than 80% Type IV graphite.  
     
     
         17 . The method according to  claim 14  wherein the wall has a matrix greater than 50% pearlite.  
     
     
         18 . The method according to  claim 14  wherein the matrix is substantially free of cementite.