According to the quality of carbon steel can be divided into ordinary carbon steels and high-quality carbon steels.
(1) ordinary carbon structural steels, also known as ordinary steel, have a wide restriction on carbon content, performance range and phosphorus, sulfur and other residual elements. In China and some countries according to the guarantee of delivery conditions are divided into three categories: Class A steel (Type a steel) is to ensure the mechanical properties of steel. The Type B steel (Type a) is the steel that guarantees the chemical composition. Special type steel (Type C steel) is a steel that guarantees both mechanical properties and chemical composition, and is often used to make more important structural parts. China's current production and use of the most is carbon content of about 0.2% A3 Steel (Group a 3rd steel), mainly used in engineering structure.
Some carbon structural steels also add trace amounts of aluminum or niobium (or other carbide-forming elements) to form nitride or carbide particles to limit grain growth, strengthen steel and save steel. In order to meet the special requirements of specialized steels, the chemical compositions and properties of ordinary carbon structural steels have been adjusted to develop a series of professional steels for ordinary carbon structural steels (such as bridges, buildings, steel bars, pressure vessels, forgings, etc.).
(2) The content of sulfur, phosphorus and other non-metallic inclusions is lower than that of high quality carbon structural steels and ordinary carbon structural steels. Depending on the carbon content and use, this type of steel is broadly divided into three categories:
① is less than 0.25%c for mild steel, especially 08f,08al with a carbon less than 0.1%, which is widely used as deep stamping parts such as automobiles and cans because of its good depth and weldability. And so on. 20G is the main material for manufacturing common boilers. In addition, low carbon steels are widely used as carburizing steels for mechanical manufacturing.
②0.25~0.60%c for medium carbon steel, more in the state of the use of quenched and manufactured machinery manufacturing industry forgings.
③ is more than 0.6%c for high carbon steel, used for making springs, gears, rolls, etc. According to the different manganese content, can be divided into ordinary manganese content (0.25~0.8%) and higher manganese content (0.7~1.0% and 0.9~1.2%) of the two steel groups. Manganese can improve the hardenability of steel, strengthen ferrite, and improve the yield strength, tensile strength and wear resistance of steel. It is usually marked "MN" after the grade of steel containing manganese, such as 15Mn, 20Mn to distinguish the normal manganese content of carbon steel.