Methods for treating a cast iron workpiece

Abstract

Examples of methods for treating a cast iron workpiece are disclosed herein. In one example of the method, a nanocrystallized microstructure at a finish surface of the cast iron workpiece is roller burnished. The roller burnishing reduces roughness of the nanocrystallized microstructure. In another example of the method, a machined, finish surface of the cast iron workpiece is deformed by rubbing the machined, finish surface against a blunt tool to form a nanocrystallized microstructure at the machined, finish surface. The machined, finish surface is cooled simultaneously with the deforming to promote nanocrystallization of the machined, finish surface.

1 . A method for treating a cast iron workpiece, the method comprising roller burnishing a nanocrystallized microstructure at a finish surface of the cast iron workpiece, thereby reducing roughness of the nanocrystallized microstructure. 
     
     
         2 . The method as defined in  claim 1  wherein the roller burnishing is accomplished with a cylindrical shaped tool or a spherical shaped tool, the cylindrical or spherical shaped tool having a polished surface with a surface roughness Rz <1 μm. 
     
     
         3 . The method as defined in  claim 2  wherein the roller burnishing is accomplished for a time ranging from about 10 seconds to about 120 seconds. 
     
     
         4 . The method as defined in  claim 1  wherein prior to the roller burnishing, the method further comprises:
 machining the cast iron workpiece to provide the finish surface thereon; and 
 deforming the finish surface of the workpiece by rubbing the finish surface against a blunt tool, thereby forming the nanocrystallized microstructure at the finish surface. 
 
     
     
         5 . The method as defined in  claim 4  wherein after the deforming and after the roller burnishing, the method further comprises:
 nitrocarburizing the cast iron workpiece, the nanocrystallized microstructure accelerating diffusion of nitrogen atoms and carbon atoms therethrough, the nitrocarburizing taking place:
 i) if the cast iron workpiece is stress relieved, for a period of time ranging from about 1 hour to about 2 hours at a temperature ranging from about 550° C. to about 570° C., or 
 ii) if the cast iron workpiece is not stress relieved, for a period of time ranging from about 5 hours to about 10 hours at a temperature ranging from about 370° C. to about 450° C. 
 
 
     
     
         6 . The method as defined in  claim 4  wherein machining is accomplished by a process selected from turning, milling, sand blasting, grit blasting, grinding, and combinations thereof. 
     
     
         7 . The method as defined in  claim 1  wherein the cast iron workpiece is selected from a rotational member of a vehicle brake, a shaft, or an engine block cylinder liner. 
     
     
         8 . A method for treating a cast iron workpiece, the method comprising:
 deforming a machined, finish surface of the cast iron workpiece by rubbing the machined, finish surface against a blunt tool, thereby forming a nanocrystallized microstructure at the machined, finish surface; and   cooling the machined, finish surface simultaneously with the deforming, thereby promoting nanocrystallization of the machined, finish surface.   
     
     
         9 . The method as defined in  claim 8  wherein the cooling is accomplished by applying a cooling gas jet to the machined, finish surface. 
     
     
         10 . The method as defined in  claim 9  wherein the cooling gas jet is at a temperature ranging from about −100° C. to about 25° C. 
     
     
         11 . The method as defined in  claim 8  wherein the cooling is accomplished by exposing the machined, finish surface to a coolant. 
     
     
         12 . The method as defined in  claim 11  wherein the coolant includes phase changing material particles to enhance the cooling. 
     
     
         13 . The method as defined in  claim 8  wherein a cooling device to perform the cooling is integrated with the blunt tool. 
     
     
         14 . The method as defined in  claim 8 , further comprising:
 nitrocarburizing the cast iron workpiece, the nanocrystallized microstructure accelerating diffusion of nitrogen atoms and carbon atoms therethrough, the nitrocarburizing taking place:
 i) if the workpiece is stress relieved, for a period of time ranging from about 1 hour to about 2 hours at a temperature ranging from about 550° C. to about 570° C., or 
 ii) if the workpiece is not stress relieved, for a period of time ranging from about 5 hours to about 10 hours at a temperature ranging from about 370° C. to about 450° C., 
   
       thereby rendering the nanocrystallized microstructure into i) a friction surface, or ii) a corrosion-resistant surface by the nitrocarburizing.