Round Steel refers to solid long steel with a round cross-section. Its specifications are expressed in diameter, unit millimeters (mm), such as "50mm", which means circular steel with a diameter of 50mm. Round steel is divided into three types: hot rolling, forging and cold drawing. The specifications of hot-rolled round steel are 5.5-250 mm. Among them: 5.5-25 mm small round steel is mostly supplied in bundles of straight strips, and is often used as steel bars, bolts and various mechanical parts; round steel larger than 25 mm is mainly used to manufacture mechanical parts, Seamless Steel Pipe billets, etc. Classification of 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, has a carbon content ranging from 0.10% to 0.30% low carbon steel is easy to accept various processing such as forging, welding and cutting. It is often used to manufacture chains, rivets, bolts, shafts, etc. (2) Carbon steel with a carbon content of 0.25% to 0.60%. There are a variety of products such as calm steel, semi-calm steel, boiling steel, etc. In addition to carbon, it can also contain a small amount of manganese (0.70% to 1.20%). According to product quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel. Good thermal processing and cutting performance, poor welding performance. The strength and hardness are higher than that of low carbon steel, while the plasticity and toughness are lower than that of low carbon steel. It can be used directly without heat treatment, and hot rolled materials or cold drawn materials, or after heat treatment. Medium-carbon steel after quenching and tempering has good comprehensive mechanical properties. The maximum hardness that can be achieved is about HRC55, HB538, and σb is 600~1100MPa. Therefore, among various uses at medium strength levels, medium carbon steel is the most widely used. In addition to being a building material, it is also widely used in the manufacturing of various mechanical parts. (3) High-carbon steel is often called tool steel, with a carbon content ranging 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, wire taps, reamers, etc. are made of steel with a carbon content of 0.90% to 1.00%.
