Carbon structural steel, the English name: carbon structural steel, carbon is about 0.05 to 0.70%, the individual can be as high as 0.90 percent. It can be divided into ordinary carbon steel and two types of high-quality carbon steel structure. Many uses, the amount of large, mainly for railways, bridges, all types of construction, manufacturing under static load of metal components and mechanical parts and weldments unimportant Usually does not require heat treatment. 1. Press the chemical composition of carbon steel by chemical composition (ie, carbon content) can be divided into low-carbon steel, carbon steel and high carbon steel. (1) low-carbon steel, also known as mild steel, carbon content of from 0.10 to 0.30 percent of low-carbon steel is easy to accept all kinds of processing such as forging, welding and cutting, commonly used in the manufacturing chain, rivets, bolts, shaft. (2) the amount of carbon in the steel of 0.25% to 0.60% carbon steel. It has killed steel, semi-killed steel, rimmed steel and other products. In addition to carbon also contain minor amounts of manganese (0.70% to 1.20%). By product quality is divided into ordinary carbon steel and quality carbon structural steel. Thermal processing and cutting good, poor welding performance. Strength, hardness higher than the low-carbon steel, while ductility and toughness lower than low carbon steel. Do not heat treated, the direct use of hot-rolled sheet, cold-drawn materials, may also be used after heat treatment. After quenching the steel has good mechanical properties. The highest attainable hardness of about HRC55 (HB538), σb is 600 ~ 1100MPa. So moderate intensity levels for various applications, carbon steel the most widely used, except as a building material, but also used extensively for the manufacture of mechanical parts. (3) high-carbon steel often called tool steel, carbon content from 0.60 to 1.70%, can be hardened and tempered. Hammers, crowbars, etc. by the carbon content of steel 0.75%; cutting tools such as wire-tapping, reamers, etc. by the carbon content of steel 0.90 to 1.00% of.