Round steel refers to a solid long steel bar with a circular cross-section. Its specifications are expressed in diameter in millimeters (mm). For example, "50mm" means round steel with a diameter of 50 mm.

Classification by process

Round steel is divided into three types: hot rolled, forged and cold drawn. The specifications of hot-rolled round steel are 5.5-250 mm. Among them: small round steel of 5.5-25 mm is mostly supplied in straight strips and bundles, and is commonly used as steel bars, bolts and various mechanical parts; round steel larger than 25 mm is mainly used to manufacture mechanical parts and seamless steel pipe blanks. wait.

Classification by chemical composition

Carbon steel can be divided into low carbon steel, medium carbon steel and high carbon steel according to its chemical composition (i.e. carbon content).

(1) Mild steel

Also known as mild steel, low carbon steel with carbon content from 0.10% to 0.30% is easy to accept various processing such as forging, welding and cutting, and is often used to make chains, rivets, bolts, shafts, etc.

(2) Medium carbon steel

Carbon steel with a carbon content of 0.25% to 0.60%. There are many products including killed steel, semi-killed steel, boiled steel and so on. In addition to carbon, it can also contain a small amount of manganese (0.70% ~ 1.20%). According to product quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel. Thermal processing and cutting performance are good, but the welding performance is poor. The strength and hardness are higher than low carbon steel, but the plasticity and toughness are lower than low carbon steel. Hot-rolled materials and cold-drawn materials can be used directly without heat treatment, or they can be used after heat treatment. Medium carbon steel after quenching and tempering has good comprehensive mechanical properties. The highest hardness that can be achieved is about HRC55, HB538, and σb is 600~1100MPa. Therefore, among various uses with medium strength levels, medium carbon steel is the most widely used. In addition to being used as building materials, it is also widely used in the manufacture of various mechanical parts.

(3) High carbon steel

Often called tool steel, it contains carbon from 0.60% to 1.70% and can be hardened and tempered. Hammers, crowbars, etc. are made of steel with a carbon content of 0.75%; cutting tools such as drills, taps, reamers, etc. are made of steel with a carbon content of 0.90% to 1.00%.

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 wider restrictions on carbon content, performance range, and content of phosphorus, sulfur and other residual elements. In China and some countries, it is divided into three categories according to the delivery guarantee conditions: Class A steel (Class A steel) is steel with guaranteed mechanical properties. Class B steel (Class B steel) is steel with guaranteed chemical composition. Special steel C-type steel is steel that ensures both mechanical properties and chemical composition. It is often used to manufacture more important structural parts. The most produced and used steel in China is A3 steel (Class A No. 3 steel) with a carbon content of about 0.20%, which is mainly used for engineering structures.

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 the steel, and save steel. In China and some countries, in order to adapt to the special requirements of professional steel, the chemical composition and properties of ordinary carbon structural steel have been adjusted, thus developing a series of ordinary carbon structural steel for professional steel (such as bridges, buildings, Steel bars, steel for pressure vessels, etc.).

(2) Compared with ordinary carbon structural steel, high-quality carbon structural steel contains lower sulfur, phosphorus and other non-metal inclusion content. According to different carbon content and uses, this type of steel is roughly divided into three categories:

① Less than 0.25% C is low carbon steel, especially 08F, 08Al, etc., which contain less than 0.10% carbon. They are widely used as deep drawing parts such as automobiles and can-making due to their good deep drawing properties and weldability. ……wait. 20G is the main material for manufacturing ordinary boilers. In addition, low carbon steel is also widely used as carburizing steel in the machinery manufacturing industry.

②0.25~0.60%C is medium carbon steel, which is mostly used in the tempered state to make parts in the machinery manufacturing industry.

③C content greater than 0.6% is high carbon steel, which is mostly used to make springs, gears, rollers, etc.

According to the different manganese content, it can be divided into two steel groups: ordinary manganese content (0.25~0.8%) and higher manganese content (0.7~1.0% and 0.9~1.2%). Manganese can improve the quench-hardenability of steel, strengthen ferrite, and increase the yield strength, tensile strength and wear resistance of steel. Usually the mark "Mn" is added after the grade of steel with high manganese content, such as 15Mn, 20Mn, to distinguish it from carbon steel with normal manganese content.

Classified by use

According to use, it can be divided into carbon structural steel and carbon tool steel.

Carbon tool steel has a carbon content between 0.65 and 1.35%. It can obtain high hardness and high wear resistance after heat treatment. It is mainly used to manufacture various tools, cutting tools, molds and measuring tools (see tool steel).

Carbon structural steel is divided into 5 grades according to the yield strength of the steel:

Q195, Q215, Q235, Q255, Q275

Material of round steel: Q195, Q235, 10#, 20#, 35#, 45#, Q215, Q345, 12Cr1Mov, 15CrMo, 304, 316, 20Cr, 40Cr, 20CrMo, 35CrMo, 42CrMo, 40CrNiMo, GCr15, 65Mn, 50Mn , 50Cr, 3Cr2W8V, 20CrMnTi, 5CrMnMo, etc.

The difference between round steel and other steel bars:

1. The appearance is different. The round steel has a smooth round shape with no lines or ribs. The surface of other steel bars has grooves or ribs. This results in a small bonding force between the round steel and the concrete, while the bonding force between the other steel bars and the concrete is small. Great adhesion.

2. The composition is different. Round steel (first-grade steel) is ordinary low carbon steel, while other steel bars are mostly alloy steel.

3. The strength is different. Round steel has low strength while other steels have high strength. That is, compared with other steel bars, round steel with the same diameter can withstand less tensile force than other steel bars, but the plasticity of round steel is smaller than that of other steel bars. Strong, that is, the round steel has a larger deformation before being pulled off, while the deformation of other steel bars before being pulled off is much smaller.