Classification by process
Round steel is divided into hot rolling, forging and cold drawing. Hot rolled round steel is 5.5-250mm in size. Among them: 5.5-25mm small round steel is mostly supplied in straight bundles, commonly used as reinforcement, bolts and various mechanical parts; Round steel larger than 25 mm, mainly used for manufacturing mechanical parts, seamless steel tube billet, etc.

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

(1) low carbon steel

Also known as mild steel, carbon content from 0.10% to 0.30% low carbon steel is easy to accept all kinds of processing such as forging, welding and cutting, often used in the manufacture of chains, rivets, bolts, shafts and so on.

(2) the medium carbon steel

Carbon steel 0.25% to 0.60% carbon. There are killed steel, semi-killed steel, boiling steel and other products. 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. Good hot working and cutting performance, poor welding performance. The strength and hardness are higher than low carbon steel, while the plasticity and toughness are lower than low carbon steel. Without heat treatment, directly use hot rolled material, cold drawn material, can also be used after heat treatment. The quenched and tempered medium carbon steel has good comprehensive mechanical properties. The highest hardness that can be achieved is about HRC55(HB538) and σb is 600 ~ 1100MPa. So in a variety of uses of moderate strength level, medium carbon steel is the most widely used, in addition to as a building material, but also a large number of used in the manufacture of various mechanical parts.

(3) high carbon steel

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