High quality carbon structural steel (GB/T699-1999):

In addition to carbon (C) elements and alloy elements containing a certain amount of silicon (Si) (generally not more than 0.40%) and manganese (Mn) (generally not more than 0.80%, higher than 1.20%) for deoxidation, there are no other alloy elements (except residual elements). The chemical composition and mechanical properties of this kind of steel must be guaranteed at the same time. The content of sulfur (S) and phosphorus (P) impurities is generally controlled below 0.035%. If it is controlled below 0.030%, it is called high-quality steel, and its brand name should be followed by "A", such as 20A; if P is controlled below 0.025%, and S is controlled below 0.020%, it is called super-quality steel, and its brand name should be followed by "E" to indicate the difference. For other residual alloying elements, such as chromium (Cr), nickel (Ni), copper (Cu), etc., which are brought into steel by raw materials, the contents are generally controlled to be less than 0.25%, 0.30% and 0.25% respectively. Some brands of manganese (Mn) content up to 1.40%, known as manganese steel.

This kind of steel relies on adjusting the carbon content (C) to improve its mechanical properties. Therefore, according to the carbon content, this kind of steel can be divided into:

Low carbon steel - generally less than 0.25% carbon content, such as 10, 20 steel, etc.

Medium Carbon Steel - Carbon content generally ranges from 0.25% to 0.60%, such as 35, 45 steel, etc.

High carbon steel - generally contains more than 0.60% carbon. This kind of steel is generally not used to manufacture steel pipes.

In fact, there is no clear limit between their carbon content.

This kind of steel has a large output and a wide range of uses. Generally, it is rolled (forged) into round, square and flat sections, plates and seamless steel pipes. It is mainly used to manufacture parts and components of general structure and mechanical structure, as well as building structural parts and pipelines for conveying fluids. According to the use requirements, sometimes heat treatment (normalizing or tempering) is needed after use. High quality carbon structural steels can be divided into three categories according to their carbon content: low carbon steels (C < 0.25%), medium carbon steels (C 0.25-0.6%) and high carbon steels (C > 0.6%).

High quality carbon structural steels are divided into two groups according to manganese content: normal manganese content (0.25% - 0.8%) and high manganese content (0.70% - 1.20%). The latter has better mechanical properties and processing properties.

1. Hot rolled sheet and strip of high quality carbon structural steel

High quality carbon structural steel hot rolled sheets and strips are used in automobile, aviation industry and other parts. Its steel grades are boiling steel: 08F, 10F, 15F; killed steel: 08, 08AL, 10, 15, 20, 25, 30, 35, 40, 45, 50. Low carbon steel plates below 25 and above 30 are medium carbon steel plates.

2. Hot rolled thick steel plate and wide steel strip of high quality carbon structural steel

High quality carbon structural steel hot rolled thick steel plate and wide steel strip are used for various mechanical structural parts. Its steel grades are low carbon steel including: 05F, 08F, 08, 10F, 10, 15F, 15, 20F, 20, 25, 20Mn, 25Mn, etc. Medium carbon steel includes: 30, 35, 40, 45, 50, 55, 60, 30Mn, 40Mn, 50Mn, 60Mn, etc. High carbon steel includes: 65, 70, 65Mn, etc. The sulphur and phosphorus content of high quality carbon structural steel is less than 0.035%, which is mainly used to manufacture more important parts. In engineering, it is generally used to produce steel wires, strands, anchors, high strength bolts and steel castings of important structures for prestressing concrete.

According to GB/T 699-1999, the grades of high-quality carbon structural steels are expressed in two digits, that is, the ten-millionths of the average carbon content in steels. For example, steel 20 represents a high quality carbon steel with an average carbon content of 0.20%. For boiling steel, F is added to the tail, such as 10F, 15F, etc. The grades of 08, 10, 15, 20 and 25 belong to low carbon steel. They have good plasticity and are easy to be drawn, stamped, extruded, forged and welded.

The grades 08, 10, 15, 20 and 25 of high quality carbon structural steels are low carbon steels, which have good plasticity and are easy to draw, stamp, extrude, forge and weld. Among them, 20 steel is widely used to make screws, nuts, washers, shafts, stamping parts, welding parts, and sometimes carburized parts. The grades of 30, 35, 40, 45, 50 and 55 belong to medium carbon steel. As the pearlite content in the steel increases, its strength and hardness are higher than before, and the hardness after quenching can be significantly increased. Among them, 45 steel is a typical steel. It has not only high strength and hardness, but also good plasticity and toughness, that is, excellent comprehensive performance. 45 steel is widely used in mechanical structure. It is often used to manufacture shafts, screw, gears, connecting rods, sleeves, keys, important screws and nuts. The grades of 60, 65, 70 and 75 belong to high carbon steel. After quenching and tempering, they not only increase strength and hardness, but also have excellent elasticity. They are often used to manufacture small springs, hairsprings, wire ropes, rolls and so on.