Method for nitriding suspension components

Abstract

A controlled nitrogen diffusion process is employed on a steel coil spring of a suspension system. One known process is that known as the Nitreg® process. Ammonia is introduced into a furnace atmosphere and nitrogen diffuses into the coil spring, creating a hardened diffusion zone which resists fatigue and fractures. The Nitreg® nitrogen diffusion process is a computer controlled menu driven process which continually monitors the process parameters. By regulating the nitriding potential, the monitored process parameters are automatically adjusted to achieve optimal results. The nitriding potential is the tendency of nitrogen to be absorbed by steel and is expressed as the ratio of the partial pressure of ammonia to the partial pressure of hydrogen. Additionally, the depth of the white compound layer can be regulated or eliminated, reducing distortions.

What is claimed is:  
     
         1 . A method for surface hardening a steel coil spring of a suspension system comprising the steps of: 
 nitriding a surface of said coil spring; and    regulating a nitriding potential in a nitriding atmosphere to control the step of nitriding said coil spring, said nitriding potential being the tendency of nitrogen to be absorbed by said steel coil spring.    
     
     
         2 . The method as recited in  claim 1  wherein the step of regulating said nitriding potential further includes monitoring at least one process parameter.  
     
     
         3 . The method as recited in  claim 1  wherein the step of nitriding said coil spring further includes introducing ammonia into said nitriding atmosphere.  
     
     
         4 . The method as recited in  claim 1  further comprising the steps of: 
 cleaning said surface of said coil spring;  
 heating said coil spring; and  
 cooling said coil spring.  
 
     
     
         5 . The method as recited in  claim 4  wherein the step of heating said coil spring includes heating said nitriding atmosphere to a temperature between 380° C. and 480° C.  
     
     
         6 . The method as recited in  claim 1  wherein the step of nitriding said coil spring produces a diffusion zone having a depth between 30μm and 100μm.  
     
     
         7 . The method as recited in  claim 1  wherein the step of nitriding said coil spring further includes forming a compound layer on said surface of said coil spring having a depth between 0 and 2μm.  
     
     
         8 . The method as recited in  claim 1  further comprising the step of shot peening said surface of said coil spring.  
     
     
         9 . The method as recited in  claim 9  wherein the surface of said coil spring is shot peened with a 0.8 mm diameter shot and a 0.3 mm diameter shot.  
     
     
         10 . A method for surface hardening a steel coil spring of a suspension system comprising the steps of: 
 cleaning said surface of said coil spring;    heating said coil spring;    nitriding a surface of said coil spring;    regulating a nitriding potential in a nitriding atmosphere to control the step of nitriding said coil spring, said nitriding potential being the tendency of nitrogen to be absorbed by said steel coil spring;    cooling said coil spring; and    shot peening said surface of said coil spring.    
     
     
         11 . A steel coil spring of a suspension system comprising: 
 a steel body portion having a surface; and    a diffusion zone produced by nitriding said surface of said coil spring by regulation of a nitriding potential.    
     
     
         12 . The coil spring as recited in  claim 11  wherein said surface of said coil spring is nitrided by introducing ammonia into a nitriding atmosphere.  
     
     
         13 . The coil spring as recited in  claim 11  wherein a nitriding atmosphere is heated to a temperature between 380° C. and 480° C.  
     
     
         14 . The coil spring as recited in  claim 11  wherein said diffusion zone has a depth between 30μm and 100μm.  
     
     
         15 . The coil spring as recited in  claim 11  wherein said coil spring further includes a compound layer having a depth between 0 and 2μm.