The carbon content is about 0.05% ~ 0.70%, and some can be as high as 0.90%. It can be divided into ordinary carbon structural steel and high-quality carbon structural steel. The former contains more impurities and is low in price, which is used in places with low requirements on performance. Its carbon content is mostly below 0.30%, manganese content is less than 0.80%, and its strength is low, but its plasticity, toughness and cold deformation performance are good. Except for a few cases, it is generally used directly without heat treatment. Made of bar steel, special-shaped steel, steel plate, etc. It has many uses and a large amount of consumption, and is mainly used in railways, bridges and various construction projects, manufacturing various metal members bearing static loads, mechanical parts and general weldments which do not need heat treatment. High-quality carbon structural steel has pure steel, few impurities and good mechanical properties, and can be used after heat treatment.