Surface hardening is a process used to increase the hardness of a material's surface while maintaining a softer, tougher interior. This technique is commonly applied to metals, such as steel, to enhance their wear resistance and fatigue strength. Methods of surface hardening include case hardening, quenching, and tempering, which alter the material's microstructure. The primary goal of surface hardening is to improve the performance and longevity of components subjected to friction and wear. By hardening the surface, parts like gears, shafts, and bearings can withstand harsher operating conditions, ultimately leading to reduced maintenance and replacement costs.