Friction brake component and method for manufacturing the same

Abstract

A ferritically nitrocarburized rotational member of a vehicle brake is disclosed, including a rotational member having a friction surface configured for braking engagement with a corresponding friction material. A compound zone is disposed at the friction surface. An exposed surface of the compound zone is exposed to an atmosphere. The area of the exposed surface includes from about 0 percent to about 14 percent graphite.

1 . A ferritically nitrocarburized rotational member of a vehicle brake, comprising:
 a rotational member, including:   a friction surface configured for braking engagement with a corresponding friction material;   a compound zone disposed at the friction surface; and   an exposed surface of the compound zone exposed to an atmosphere wherein an area of the exposed surface includes from about 0 percent to about 14 percent graphite.   
     
     
         2 . The rotational member as defined in  claim 1  wherein the area of the exposed surface includes from about 1 percent to about 10 percent graphite. 
     
     
         3 . The rotational member as defined in  claim 1  wherein the area of the exposed surface includes from about 2 percent to about 5 percent graphite. 
     
     
         4 . The rotational member as defined in  claim 1  wherein the area of the exposed surface includes from about 3 percent to about 14 percent graphite. 
     
     
         5 . The rotational member as defined in  claim 1  wherein the rotational member is formed from gray cast iron, steel, or stainless steel. 
     
     
         6 . The rotational member as defined in  claim 1  wherein the rotational member further comprises a brake rotor, a brake drum, or combinations thereof. 
     
     
         7 . The rotational member as defined in  claim 1  wherein the corresponding friction material exhibits a wear of less than 0.4 mm per 1000 stops at about 350° C. 
     
     
         8 . The rotational member as defined in  claim 1  wherein the compound zone exhibits a hardness of between about 56 HRC and about 64 HRC. 
     
     
         9 . The rotational member as defined in  claim 1  wherein the rotational member exhibits a coefficient of friction of at least 0.32. 
     
     
         10 . The rotational member as defined in  claim 1  wherein less than 15 percent of the exposed surface exhibits visible red rust after 1 week in humid air with a temperature of at least about 10° C. (50° F.). 
     
     
         11 . A method for increasing useful life of a rotational member of a vehicle brake, comprising removing graphite flakes from a friction surface of the rotational member prior to nitrocarburizing the friction surface. 
     
     
         12 . The method as defined in  claim 11  wherein removing the graphite flakes is accomplished by a process selected from sand blasting, grit blasting, grinding, and combinations thereof. 
     
     
         13 . The method as defined in  claim 11  wherein graphite comprises from about 0 percent to about 14 percent of the friction surface after removing the graphite flakes. 
     
     
         14 . The method as defined in  claim 11  wherein nitrocarburizing includes a gas nitrocarburizing process, a plasma nitrocarburizing process, or a salt bath nitrocarburizing process. 
     
     
         15 . The method as defined in  claim 11  wherein the nitrocarburizing comprises:
 immersing at least the friction surface of the rotational member into a nitrocarburizing salt bath; and then immersing the at least the friction surface of the rotational member into an oxidizing salt bath. 
 
     
     
         16 . A rotational member formed by the method of  claim 11  wherein the rotational member is formed from gray cast iron, and the rotational member includes a brake rotor, a brake drum, or a combination thereof. 
     
     
         17 . The rotational member as defined in  claim 16  wherein a corresponding friction material exhibits wear of less than 0.4 mm per 1000 stops at 350° C. 
     
     
         18 . The rotational member as defined in  claim 16  wherein a compound zone exhibits hardness of between about 56 HRC and about 64 HRC. 
     
     
         19 . The rotational member as defined in  claim 16  wherein the friction surface of the rotational member exhibits a coefficient of friction of at least 0.32. 
     
     
         20 . The rotational member as defined in  claim 16  wherein less than 15 percent of an exposed portion of the friction surface exhibits visible red rust after 1 week in humid air with a temperature of at least about 10° C. (50° F.).