Alloy structural steel (GB/T3077-1999) is produced by adding one or more alloy elements to carbon structural steel to enhance its mechanical properties, toughness, and hardenability. Products made from this steel typically require heat treatment, such as normalizing or tempering. Before use, the components are usually treated with tempering or surface chemical processes (carburizing, nitriding, etc.), surface quenching, or high-frequency quenching. Therefore, based on the chemical composition (mainly carbon content), heat treatment methods, and applications, this type of steel can be broadly categorized into three types: carburized, tempered, and nitrided steels.