Iron is the main component of steel. Iron carbon alloy with carbon content less than 2.11% is called steel. But industrial carbon steel has other elements besides carbon, such as silicon, manganese, phosphorus, sulfur, etc. these elements are divided into deoxidizing elements (such as silicon, manganese, etc.), impurity elements (such as smelting the undeleted phosphorus, sulfur, etc.) and alloy elements (such as molybdenum, chromium, rare earth, etc. added to improve performance). (1) Carbon impact Carbon is the main element that determines the structure and properties of carbon steel after slow cooling. In general, the carbon content increases, the strength increases and the elongation decreases. In addition, the properties of different structures (ferrite, cementite and pearlite) are obviously different. With the increase of carbon content, the corrosion resistance of carbon steel is decreased, and the weldability and cold workability (stamping and drawing) of carbon steel are also decreased. (2) The effect of manganese The content of manganese in carbon steel is generally 0.25% ~ 0.80%. In carbon steel with high manganese content, the content of manganese can reach 1.2%. In carbon steel, manganese is a beneficial element. For killed steel, manganese can improve the deoxidization effect of silicon and aluminum, and can also combine with sulfur to form manganese sulfide, so as to eliminate the harmful effect of sulfur in steel to a large extent. Manganese has a good effect on the mechanical properties of carbon steel. It can improve the hardness and strength of the steel after hot rolling. When the manganese content is not high, the surface shrinkage and impact toughness of carbon steel can be slightly increased or not reduced. (3) Influence of silicon Silicon content in carbon steel is less than or equal to 0.5%. Silicon is also a useful element in steel. In the boiling steel, the silicon content is very low. Silicon is added to the killed steel as a deoxidizing element. Silicon increases the fluidity of liquid steel. In addition to forming non-metallic inclusions, silicon is soluble in ferrite. However, when the silicon content exceeds a certain value, the impact toughness of the material decreases significantly. (4) Effect of sulfur Generally speaking, sulfur is a harmful element, which mainly comes from pig iron. The harm of sulfur is the cracking of steel during hot working, that is to say, the so-called hot brittleness is caused by the serious segregation of sulfur. Even if the sulfur content is not very high, there will be (Fe + FES) eutectic. Generally, manganese is added to prevent hot brittleness. Sulfur affects the mechanical properties of steel by forming sulfide inclusions. The influence of sulfur on the mechanical properties of steel is not only related to the content, but also to the size, shape and structure of inclusions. (5) Effect of phosphorus Generally speaking, phosphorus is a harmful impurity element, which comes from steel-making raw materials such as ore and pig iron. Phosphorus has a considerable solubility in pure iron. Phosphorus can improve the strength of steel, but the toughness of steel decreases, especially the brittle transition temperature of steel increases sharply, that is to say, to improve the cold brittleness of steel. In the steel with low carbon content, phosphorus is less harmful to cold embrittlement. In this case, phosphorus can be used to improve the strength of steel. In addition, phosphorus can improve the atmospheric corrosion resistance and reduce the adhesion of hot-rolled sheet.