This type of steel must ensure both chemical composition and mechanical properties. Its grade uses two digits to express the mass fraction of the average carbon in the steel in ten thousand (ωс*10000). For example, 45 steel means that the average carbon mass fraction in the steel is 0.45%; 08 steel means that the average carbon mass fraction in the steel is 0.08%.
High-quality carbon structural steel is mainly used to make machine parts. Generally, heat treatment is required to improve mechanical properties. Depending on the carbon mass fraction, it has different uses. 08, 08F, 10, and 10F steel have high plasticity and toughness, excellent cold-forming performance, and welding performance. It is often cold-rolled into thin plates and used to make instrument casings and cold stamping parts on cars and tractors, such as car bodies and tractors. Cabs, etc.; 15, 20, and 25 steel are used to make carburized parts that are smaller in size, lighter in load, wear-resistant on the surface, and have low core strength requirements, such as piston pins, templates, etc.; 30, 35, 40, 45 and 50 steel have good comprehensive mechanical properties after heat treatment (quenching + high-temperature tempering), that is, they have high strength, high plasticity and toughness, and are used to make shaft parts. For example, 40 and 45 steel are often used in manufacturing Crankshafts, connecting rods of automobiles and tractors, general machine tool spindles, machine tool gears, and other shaft parts with little stress; 55, 60, and 65 steel have high elastic limits after heat treatment (quenching + medium temperature tempering) and are often used in manufacturing Springs with low load and small size (section size less than 12~15mm), such as pressure regulating and speed regulating springs, plunger springs, cold coil springs, etc.
