1. Carbon (C): The carbon content in the steel increases, the yield point and tensile strength increase, but the plasticity and impact properties decrease. When the carbon content exceeds 0.23%, the welding performance of the steel deteriorates, so it is used for welding Low-alloy structural steel, the carbon content generally does not exceed 0.20%. High carbon content will also reduce the atmospheric corrosion resistance of steel, and high carbon steel in the open stockyard is easy to rust; in addition, carbon can increase the cold brittleness and aging sensitivity of steel.
2. Silicon (Si): Silicon is added as a reducing agent and deoxidizer in the steelmaking process, so the killed steel contains 0.15-0.30% silicon. If the silicon content in the steel exceeds 0.50-0.60%, silicon is considered an alloying element. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, so it is widely used as spring steel. Adding 1.0-1.2% silicon in quenched and tempered structural steel can increase the strength by 15-20%. The combination of silicon and molybdenum, tungsten, chromium, etc. has the effect of improving corrosion resistance and oxidation resistance, and can be used to manufacture heat-resistant steel. Low-carbon steel containing 1-4% silicon has extremely high magnetic permeability and is used in the electrical industry to make silicon steel sheets. The increase in the amount of silicon will reduce the welding performance of the steel.
3. Manganese (Mn): In the steelmaking process, manganese is an excellent deoxidizer and desulfurizer. Generally, the manganese content in steel is 0.30-0.50%. When more than 0.70% is added to carbon steel, it is considered "manganese steel". Compared with ordinary steel, it not only has sufficient toughness, but also has higher strength and hardness, which improves the hardenability of steel and improves the thermal processing performance of steel. For example, the yield point of 16Mn steel is 40% higher than that of A3. Steel containing 11-14% manganese has extremely high wear resistance, and is used for excavator buckets, ball mill liners, etc. The increase of manganese content will weaken the corrosion resistance of steel and reduce the welding performance.
4. Phosphorus (P): In general, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, deteriorates welding performance, reduces plasticity, and deteriorates cold bending performance. Therefore, it is generally required that the phosphorus content in steel is less than 0.045%, and the requirement for high-quality steel is lower.
5. Sulfur (S): Sulfur is also a harmful element in general. It causes hot brittleness of steel, reduces the ductility and toughness of steel, and forms cracks during casting and rolling. Sulfur is also detrimental to welding performance and reduces corrosion resistance. Therefore, it is generally required that the sulfur content is less than 0.055%, and that of high-quality steel is less than 0.040%. Adding 0.08-0.20% sulfur in steel can improve machinability, and it is generally called free-cutting steel.
