Surface hardening treatment in sheet metal processing is aimed at improving the mechanical properties of the sheet metal surface, such as hardness, wear resistance, and fatigue strength, while maintaining the ductility and toughness of the core material. One of the widely used surface hardening methods is case hardening. Case hardening includes processes like carburizing, nitriding, and carbonitriding. In carburizing, the sheet metal is heated in a carbon-rich atmosphere, such as a gas carburizing furnace or a salt bath containing carbonaceous materials. Carbon diffuses into the surface layer of the sheet metal, increasing its carbon content. After carburizing, the part is quenched and tempered to form a hard, wear-resistant surface layer while keeping the core soft and tough. Carburizing is commonly used for sheet metal components that require high surface hardness and wear resistance, such as gears, shafts, and cams in automotive and machinery applications.

　　Nitriding is another effective surface hardening process. In nitriding, the sheet metal is exposed to a nitrogen-rich environment at a relatively low temperature. Nitrogen atoms diffuse into the surface layer of the metal, forming hard nitride compounds. Nitriding offers several advantages, including excellent wear resistance, corrosion resistance, and fatigue strength. It does not cause significant distortion of the sheet metal part, making it suitable for components with tight dimensional tolerances. Nitrided sheet metal is often used in high-precision machinery parts, such as precision bearings and cutting tools. Carbonitriding combines the features of carburizing and nitriding, where both carbon and nitrogen are introduced into the surface layer of the sheet metal. This process can achieve a good balance between hardness, wear resistance, and toughness, and is used for components that require a combination of these properties.

　　Induction hardening is also a popular surface hardening technique. In induction hardening, the sheet metal is placed in a high-frequency electromagnetic field. The electromagnetic field induces eddy currents in the surface layer of the metal, which generate heat due to the resistance of the metal. The rapid heating causes the surface layer to reach a high temperature, and then it is quenched immediately to harden the surface. Induction hardening is a fast and efficient process that can be precisely controlled to achieve the desired depth of hardening. It is commonly used for hardening the surface of sheet metal parts with specific geometric shapes, such as the edges and corners of brackets and the surfaces of shafts. Surface hardening treatment not only extends the service life of sheet metal components but also improves their performance in various applications, reducing the need for frequent replacement and maintenance.