Case hardening is a finishing process that increases the hardness of a component's surface. It can be used on some of the most commonly-used metals such as tool steel, stainless steel, cast iron, alloy steel and carbon steel.
During the case hardening process, the material is heated to such a temperature where the structure of its surface starts to be affected. When this temperature is achieved, the material is rapidly cooled in a process known as quenching, whereby it is brought into contact with a liquid such as water or oil. This causes the material's surface to harden, providing resistance to wear and corrosion; however, the interior will not be affected.
Depending on the case hardening process used, secondary operations such as grinding may be required post-production, which will increase the overall cost. Case hardening is a common finishing technique for parts such as gears and tools, and can be used to extend the lifespan of the part in question.