Quality carbon structural steel is the carbon content less than 0.8% of carbon steel, this steel contains 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 not more than 0.40%), manganese (Mn) (generally not more than 0.80 % to 1.20% may be higher) alloying elements, but without other alloying elements (except for the residual element). Such steels must also ensure that the chemical composition and mechanical properties. The sulfur (S), phosphorus (P) the general control of impurity elements 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 - generally less than 0.25% carbon content, 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 typically greater than 0.60%. Such is generally not used in the manufacture of steel pipe.

In fact, the carbon content between them, and no clear boundaries.

Such a large steel production, uses a wider, more generally rolling (forging) made ​​of round, square, flat and other profiles, plates and seamless steel pipe. Mainly for the manufacture of the general structure and mechanical parts and components and building structures and pipe conveying fluid. According to requirements, and sometimes need to heat treatment (normalizing or quenching and tempering) before use.