Carburizing is often used to restore or enhance the percentage of carbon in steel for the purpose of increasing its hardenability.
This process may be used to create a “case” hardenability, whereby the outer surface containing a higher level of carbon than the core, results in an elevated hardness case depth while the core remains lower where the carbon has not diffused into the metal. The high magnification images shown here depict gears that required such a case depth, seen as a difference in gray coloration, for increased wear resistance and serviceability.