Carbon steel: Steel with a carbon content of less than 2.11% and no specially added alloying elements is called carbon steel, or carbon steel for short.
Effects of common elements on steel properties
In addition to the two main elements of iron and carbon in carbon steel, there are always certain impurities in steel-making raw materials, and some impurities are also brought in during the smelting process, such as Si, Mn, P, S, non-metallic inclusions and oxygen, Nitrogen, hydrogen and other gases. They have a certain impact on the performance and quality of steel.
(1) Manganese (Mn). Manganese mainly comes from steelmaking deoxidizers. The manganese remaining in the steel after deoxidation can be dissolved in ferrite and cementite, improving the strength and hardness of the steel. In addition, manganese also forms MnS with sulfur, thereby reducing the harmful effects of sulfur on steel. Therefore, manganese is a beneficial element in steel, and its content is generally 0.25% to 0.80%.
(2) Silicon (Si). Silicon is an element that remains in the steel after the deoxidation reaction with ferrosilicon deoxidizer in the later stage of steelmaking. Silicon can dissolve in ferrite and has a certain strengthening effect on steel, so silicon is a beneficial element in steel. However, due to its small content, its strengthening effect is not great and should generally be controlled within 0.17% to 0.37%.
(3) Sulfur (S). Sulfur is a harmful element brought into steel by pig iron and fuel. It forms a compound FeS with iron in steel. FeS and iron form a eutectic (Fe+FeS) with a low melting point (985°C). When the steel is heated to 1000-1200°C for rolling or forging, the eutectic distributed along the grain boundaries has melted, and the connections between the grains are destroyed, causing the steel to crack. This phenomenon is called thermal brittleness. Therefore, sulfur is a harmful element in steel, and its content must not exceed 0.05%.
(4) Phosphorus (P). Phosphorus is a harmful element brought into steel by pig iron. Part of the phosphorus dissolves in ferrite to form a solid solution, and part of it forms a very brittle compound Fe3P during crystallization, causing the plasticity and toughness of steel to drop sharply at low temperatures (generally below 100°C). This phenomenon is called cold brittleness. When the phosphorus content in steel reaches 0.10%, cold brittleness becomes serious. Therefore, phosphorus is a harmful element in steel. Generally, the phosphorus content in steel is limited to less than 0.04%.
(5) Non-metallic inclusions. Non-metallic inclusions in steel include oxides, sulfides and silicates. These inclusions are produced by the steelmaking reaction and cannot be completely eliminated, or are brought in from refractory materials such as slag, furnace body, and ingot casting equipment. Non-metallic inclusions reduce the strength and plasticity of steel, so the fewer inclusions, the better the quality of the steel.