Carbon
Carbon can affect and determine various physical and chemical properties and mechanical properties of steel, such as strength, plasticity and welding performance, and also has a direct impact on heat treatments such as quenching and annealing of steel. Carbon can form carbides with some other elements in steel, and carbides are a metallographic structure of steel. Carbon has a greater affinity for oxygen. Under certain conditions, the reaction between carbon and oxygen is more active than the reaction between iron and oxygen, so it is often used as a reducing agent and deoxidizer in the steelmaking process. Carbon is also a tempering agent in heat treatment. During the oxidation process of molten steel, the interaction between carbon and oxygen generates CO, which causes the molten steel to boil and stir, so that the composition and temperature of the molten steel can be uniform. In addition, boiling can also purify the molten steel, so that inclusions and gases can be better removed.
Silicon
In the steelmaking process, silicon is also often used as a reducing agent and deoxidizer. Silicon exists in ferrite or austenite in steel in the form of solid solution. It can improve the strength of the solid solution in steel and has a strong effect on the cold working deformation hardening rate. At the same time, it can also reduce the corrosion resistance of steel to a certain extent. A certain amount of silicon and a certain amount of carbon in steel, with an appropriate amount of manganese, can greatly improve the yield limit and tensile limit after quenching and tempering. It is often used to make high-load spring materials. High-silicon low-carbon or high-silicon ultra-low-carbon steel has good magnetic permeability, high resistance and small coercive force, and low core loss. It is often used to make silicon steel sheets. High silicon is combined with alloy elements such as Mo, W, and Cr, and is also often used in the production of stainless steel and heat-resistant steel.
Manganese
Manganese is a good deoxidizer and desulfurizer. Almost all steels contain a certain amount of manganese. It can eliminate and weaken the hot brittleness of steel caused by sulfur, thereby improving the hot working performance of steel. Manganese and iron form a solid solution, which can improve the hardness and strength of ferrite or austenite in steel. At the same time, it is a carbide-forming element and can enter cementite to replace a part of iron atoms. Manganese can strongly increase the hardenability of steel; when the manganese content is high, it tends to coarsen the steel grains and increase the temper brittleness of the steel; when the cooling is improper after casting, rolling or forging, white spot defects are easily generated. In addition, manganese reduces the thermal conductivity of steel and increases its linear expansion coefficient. Therefore, high-manganese steel ingots or billets should be heated and cooled slowly to avoid excessive internal stress and cracking. This is especially important when the cross-section is large. As an alloying element, manganese has the characteristics of relatively abundant resources and diverse performance. It has been widely used in steel.
