A carbon steel. Carbon is about 0.05% to 0.70%, 0.90% up to the individual. Can be divided into ordinary carbon steel and quality carbon structural steel categories. The former contains impurities, low price, performance for less demanding areas, the majority of its carbon content of 0.30 percent, manganese does not exceed 0.80%, lower strength, but the ductility, toughness, cold deformation good. With few exceptions, for the heat treatment is generally not used directly. Made more of steel, shaped steel, steel and so on. Use a lot, a great amount, mainly for railways, bridges, all kinds of construction projects, manufacturing all kinds of metal to withstand static load without heat treatment of the important components and mechanical parts and general soldering parts. Quality carbon structural steel steel pure, less impurities, mechanical properties, and can be heat-treated before use. According to manganese content is divided into ordinary manganese content (less than 0.80%) and high manganese content (0.80% ~ 1.20%) groups. Carbon content of 0.25% or less, and more directly without heat treatment or carburizing, carbonitriding and other processing, manufacturing, small gears, shafts, piston pins, etc.; carbon content of 0.25% to 0.60%, a typical steel No. There 40,45,40 Mn, 45Mn, and many more after quenching, manufacturing all kinds of mechanical parts and fasteners, etc.; more than 0.60% carbon, such as 65,70,85,65 Mn, 70Mn, and many more as spring steel to use. Such steel is mainly to ensure that the mechanical properties, so the grades reflect its mechanical properties, with Q + digits, including "Q" is the yield point "bend" the pinyin word prefix numbers indicate the yield point value, such as Q275, said yield point 275Mpa. If the label behind the letter grades A, B, C, D, is that just a different level of quality, including S, P in order to reduce the amount, in order to improve the quality of steel. If back in Grade marked the letter "F" was boiling steel, marked "b" for the semi-killed steel, not marked "F" or "b" who is killed steel. For example, Q235-A · F that yield point 235Mpa Class A boiling steel, Q235-C that yield point 235Mpa of C-level-killed steel carbon steel generally not heat treated, and in the supply of state directly. Usually Q195, Q215, Q235 mass fraction of low-carbon steel, welding performance, plasticity, toughness, a certain intensity, often rolled into a sheet, steel, welded steel pipes, etc., for bridges, buildings and other structures and production of common screws, nuts and other parts. Q255 and Q275 slightly higher mass fraction of carbon steel, high strength, ductility, toughness, can be welded, usually rolled into steel, strip steel and steel for structural parts and manufacturing simple mechanical linkage, gears, coupling section, marketing and other parts