Case hardening is a heat treatment process used to harden the surface of metal parts while maintaining a softer, ductile interior. This technique enhances wear resistance and durability, making it ideal for components like gears and shafts. The process typically involves heating the metal and then quenching it in a hardening medium, such as oil or water. There are various methods of case hardening, including carburizing, nitriding, and carbonitriding. Each method introduces different elements into the surface layer of the metal, resulting in varying properties. This treatment is commonly used in industries where parts are subjected to high stress and friction.