1. Carbon (C): As the carbon content in 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.
High carbon content will also reduce the atmospheric corrosion resistance of steel, and the 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 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 to quenched and tempered structural steel can increase the strength by 15-20%.
3. Sulfur (S): Sulfur is also a harmful element under normal circumstances. It causes hot brittleness of steel, reduces the ductility and toughness of steel, and causes cracks during forging and rolling. Sulfur is also detrimental to weldability and reduces corrosion resistance. Therefore, it is usually required that the sulfur content is less than 0.055%, and that of high-quality steel is less than 0.040%.
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 usually required that the phosphorus content in steel is less than 0.045%, and the requirement for high-quality steel is lower.
5. Manganese (Mn): In the process of steelmaking, manganese is a good 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". 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 weakens the corrosion resistance of steel and reduces the welding performance.
