Carbon steel can be divided into ordinary carbon structural steel and high-quality carbon structural steel. The former has many impurities and low price. When it is used in places with low performance requirements, its carbon content is mostly below 0.30%, and its manganese content is less than 0.80%. Its strength is relatively low, but its plasticity, toughness and cold deformation performance are good. Except for a few cases, heat treatment is generally not carried out and directly used. And It is used to make steel bars, shaped steel, steel plate, etc. It is mainly used in railway, bridge and all kinds of construction projects to manufacture all kinds of metal components bearing static load and unimportant mechanical parts and general weldments that do not need heat treatment. High quality carbon structural steel is pure, with few impurities and good mechanical properties. It can be used after heat treatment.
1. Classification by chemical composition
Carbon steel can be divided into low carbon steel, medium carbon steel and high carbon steel according to chemical composition (i.e. carbon content). (1) low carbon steel, also known as mild steel, contains carbon from 0.10% to 0.30%. Low carbon steel is easy to accept all kinds of processing such as forging, welding and cutting. It is often used to make chains, rivets, bolts, shafts, etc. (2) carbon content of medium carbon steel is 0.25% ~ 0.60% . There are killed steel, semi killed steel, boiling steel and other products. In addition to carbon, it can also contain a small amount of manganese（ 0.70% ~ 1.20% ）(3) high carbon steel is often called tool steel, with carbon content from 0.60% to 1.70% , which can be hardened and tempered. Hammers, crowbars, etc.
2. Classification by steel quality
According to the quality of steel, it can be divided into ordinary carbon steel and high-quality carbon steel. (1) ordinary carbon structural steel, also known as ordinary carbon steel, has a wide range of restrictions on carbon content, performance range and content of phosphorus, sulfur and other residual elements. In China and some countries, in order to meet the special requirements of professional steel, the chemical composition and properties of common carbon structural steel are adjusted, so a series of professional steel of common carbon structural steel (such as bridge, building, steel bar, pressure vessel steel, etc.) are developed. (2) high quality carbon structural steel is widely used as deep drawing parts such as automobile and can making due to its good deep drawing and weldability Wait. 20G is the main material for making ordinary boilers. In addition, low carbon steel is widely used as carburizing steel in machinery manufacturing industry.