Definition of quality carbon structural steel 
 Quality carbon structural steel is the carbon content of less than 0.8% carbon steel, the steel contained sulfur, phosphorus and non-metallic inclusions less than carbon steel, the more excellent mechanical properties. Quality carbon structural steel (GB/T699-1999): steel, in addition to containing carbon (C) elements and a certain amount of oxygen and silicon (Si) (generally no more than 0.40%), manganese (Mn) (generally not more than 0.80 %, 1.20% higher available) alloying elements, but without other alloying elements (except for residual elements). Such steel must also ensure that the chemical composition and mechanical properties. The sulfur (S), phosphorus (P) impurity elements is generally controlled at 0.035% or less. If the control is called below the 0.030% senior high-quality steel, the grade should be added after "A", such as 20A; if P control of 0.025% or less, S 0.020% below control, said the super high-quality steel, the grade should be followed Add "E" to show the difference. For raw materials into steel by the remnants of other alloying elements such as chromium (Cr), Nickel (Ni), copper (Cu) content such as the general control of Cr ≤ 0.25%, Ni ≤ 0.30%, Cu ≤ 0.25%. Some grades of manganese (Mn) content reached 1.40%, known as manganese steel. Such adjustment is to rely on carbon steel (C) the amount to improve the mechanical properties of steel, therefore, according to the level of carbon content, these steels can be divided into: low carbon steel - carbon content generally less than 0.25%, such as 10, 20 steel; the carbon - carbon content is generally between 0.25 to 0.60%, such as 35,45 steel; high-carbon steel - carbon content is generally greater than 0.60%. Such is generally not used in the manufacture of steel pipe. In fact, they between carbon content and no clear boundaries. Such a large steel production, uses a wider, more general rolling (forging) made of round, square, flat and other profiles, sheets and seamless. Mainly for the manufacture of general structure and mechanical parts and components and structural parts and transmission fluid pipe. According to requirements, and sometimes need to heat treatment (normalizing or quenching and tempering) before use. 
 Classification of high-quality carbon structural steel 
 Quality carbon structural steel according to carbon content can be divided into three categories: low carbon steel (C ≤ 0.25%), medium carbon steel (C of 0.25-0.6%) and high-carbon steel (C> 
 Quality carbon structural steel 
 0.6%). Quality carbon structural steel by manganese content divided into the normal manganese content (Mn 0.25% -0.8%) and high manganese content (Mn 0.70% -1.20%) groups, which have better mechanical performance and processing performance. 1, high-quality carbon structural steel hot-rolled steel sheet and strip quality hot-rolled carbon steel sheet and strip for the automotive, aviation industry and other parts. The steel grades of boiling steel: 08F, 10F, 15F; killed steel: 08,08 AL, 10,15,20,25,30,35,40,45,50. 25 and 25 following a low-carbon steel 30 and 30 above the steel plate. 2, high-quality carbon structural steel plate and wide strip hot-rolled carbon quality steel plate and hot rolled wide strip for a variety of mechanical parts. The steel grades of low carbon steel, including: 05F, 08F, 08,10 F, 10,15 F, 15,20 F, 20,25,20 Mn, 25Mn, etc.; in carbon steel, including: 30,35,40,45,50, 55,60,30 Mn, 40Mn, 50Mn, 60Mn, etc.; high carbon steel, including: 65,70,65 Mn and so on. 
 The use of high-quality carbon structural steel 
 High-quality carbon structural steel parathion content of less than 0.035%, mainly used to make the more important parts. According to GB / T 699-1999, quality carbon structural steel grades with two digits, that is, the average carbon content of steel in the extreme digits. For example, 20 carbon steel, said the average amount of 0.20% of high-quality carbon steel. For the boiling steel in the tail with F, such as 10F, 15F, etc. 08,10,15,20,25 and other grades are low carbon steel, the plasticity good, easy-to-drawing, stamping, extrusion, forging and welding. Quality carbon structural steel grades are in 08,10,15,20,25 and other low-carbon steel, the plasticity good, easy-to-drawing, stamping, extrusion, forging and welding. 20 steel the most widely used to manufacture screws, nuts, washers, small axes and stamping parts, welding parts, also sometimes used in the manufacture carburizing parts. 30,35,40,45,50,55 and other brands are in carbon steel, because steel pearlite content increased, the strength and hardness compared with the previous increase, the hardness after quenching can be significantly increased. Among them, the 45 most typical of steel, it is not only strength, hardness, and both good ductility and toughness, that is excellent overall performance. 45 steel in the mechanical structure of the most widely used to manufacture shaft, screw, gear, connecting rod, sleeve, keys, screws and nuts so important. 60,65,70,75 and other grades are high carbon steel. They have been hardened, tempered only the strength, hardness, and good elasticity, used to create a small spring, spring, wire rope, roller, etc.