1. According to the mass percentage of carbon content in steel:

Low carbon steel (C:≤0.25%), also known as mild steel, low carbon steel is easy to accept a variety of processing such as forging, welding and cutting. Commonly used in the manufacture of chains, rivets, bolts, shafts, etc.

Medium carbon steel (0.25% < C≤0.6%), there are many products such as killed steel, semi-killed steel, boiling steel and so on. According to quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel. The hot working and cutting properties of medium carbon steel are good, but the weldability is poor. The strength and hardness are higher than low carbon steel, while the plasticity and toughness are lower than low carbon steel. Hot-rolled and cold-drawn materials can be used directly without heat treatment, and can also be used after heat treatment. The medium carbon steel after quenching and tempering has good comprehensive mechanical properties. Therefore, in the various uses of medium strength level, medium carbon steel has obtained the most extensive application, in addition to as a building material, but also a large number of used in the manufacture of various types of mechanical parts.

High carbon steel (C: > 0.6%) is often used as tool steel, carbon content from greater than 0.60 to 1.70%, can be quenched and tempered. The higher the carbon content, the greater the hardness and strength, but the lower the plasticity. (In addition, iron-carbon alloys with a carbon content of 2.1% to 4.5% are generally referred to as cast iron.)

2. According to the content of impurity elements in steel (mainly the content of impurity sulfur and phosphorus) : 

ordinary carbon steel, high-quality carbon steel, senior high-quality carbon steel.

3. According to the use of steel products:

Carbon structural steel: mainly used in Bridges, ships, building components, machine parts and so on.

Carbon tool steel: mainly used for cutting tools, molds, measuring tools, etc.