Carbon is a non-metallic element with the chemical symbol C. It is stable at room temperature, not easily reacted, has very low toxicity to humans, and can even be safely ingested in the form of graphite or activated charcoal, and is located in the second cycle of the periodic table in group IVA.

Carbon is a very common element that is widely found in many forms in the atmosphere and crust of the earth and in living things. The Latin word Carbonium means 'coal, charcoal'. Carbon is structurally diverse and can exist in monomers with a variety of properties, such as crystalline carbon, amorphous carbon and transition carbon.

Carbon monomers have long been recognized and used, and a series of compounds of carbon - organic matter is the basis of life. Carbon also has a variety of allotropes, such as diamond, graphite, graphene, fullerene, etc. These allotropes are widely used in aerospace, medical, petrochemical, defense and other fields. In addition, carbon is one of the components of pig iron, mature iron and steel. Carbon is able to chemically self-incorporate to form a large number of compounds and is a biologically and commercially important molecule. The vast majority of molecules in living organisms contain carbon.

Carbon is the main alloying element in steel materials, so steel materials can also be called iron-carbon alloys. The main role of carbon in steel is:

1. Formation of solid solution organization, improve the strength of steel, such as ferrite, austenite organization, are dissolved in carbon;

2. The formation of carbide organization, can improve the hardness and wear resistance of steel. Such as carburite, that is, Fe3C, is the carbide organization.

Therefore, carbon in steel, the higher the carbon content, the higher the strength and hardness of steel, but the plasticity and toughness will be reduced; conversely, the lower the carbon content, the higher the plasticity and toughness of steel, its strength and hardness will be reduced.

Therefore, the level of carbon content determines the use of steel: low carbon steel (carbon content <0.25%), generally used as profiles and stamping materials; medium carbon steel (carbon content <0.6%), generally used as mechanical parts; high carbon steel (carbon content > 0.7%), generally used as tools, cutting tools and molds.