Carbonitriding is a heat treatment process used to enhance the surface hardness and wear resistance of metals, particularly steel. It involves the introduction of both carbon and nitrogen into the surface layer of the material. This is typically achieved by heating the metal in a gas atmosphere containing ammonia and a carbon source, allowing the elements to diffuse into the surface. The process results in a hard, wear-resistant layer that improves the performance of components subjected to high stress and friction. Carbonitriding is commonly used in the automotive and manufacturing industries for parts like gears, shafts, and fasteners, where durability is essential.