Effect of chemical elements on properties of steel

1. Carbon (c): with the increase of carbon content in steel, the yield point and tensile strength increase, but the plasticity and impact decrease. When the carbon content is more than 0.23%, the welding performance of steel will deteriorate. Therefore, the carbon content of low alloy structural steel used for welding is generally not more than 0.20%. The high carbon content can also reduce the atmospheric corrosion resistance of steel, and the high carbon steel in the open yard is easy to rust; in addition, carbon can increase the cold brittleness and aging sensitivity of steel.

2. Silicon (SI): in the process of steelmaking, silicon is added as reducing agent and deoxidizer, so killed steel contains 0.15-0.30% silicon. If the silicon content in steel is more than 0.50-0.60%, silicon is regarded as alloy 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 the quenched and tempered structural steel can increase the strength by 15-20%. Silicon and molybdenum, tungsten, chromium etc

It can improve corrosion resistance and oxidation resistance, and can make heat-resistant steel. Low carbon steel with silicon content of 1-4% and high permeability is used in the electrical industry to make silicon steel sheet. The increase of silicon content will decrease the weldability of steel.

3. Manganese (MN): in the process of steelmaking, manganese is a good deoxidizer and desulfurizer. Generally, the content of manganese in steel is 0.30-0.50%. When more than 0.70% of carbon steel is added, it will be regarded as "manganese steel". Compared with the general steel, the steel has not only enough toughness, but also higher strength and hardness, which can improve the hardenability of the steel and improve the hot working performance of the steel. For example, the yield point of 16Mn steel is 40% higher than that of A3 steel. The steel containing 11-14% manganese has very high wear resistance, which is used for excavator bucket, ball mill liner, etc. The increase of manganese content weakens the corrosion resistance of steel and reduces the weldability.

4. Phosphorus (P): in general, phosphorus is a harmful element in steel. It can increase the cold brittleness of steel, make the welding performance worse, reduce the plasticity, and make the cold bending performance worse. 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. The hot brittleness of the steel is produced, the ductility and toughness of the steel are reduced, and cracks are caused during forging and rolling. Sulfur is also detrimental to welding performance, reducing corrosion resistance. Therefore, the sulfur content is generally required to be less than 0.055%, and the high-quality steel is required to be less than 0.040%. Adding 0.08-0.20% sulfur to the steel can improve the machinability, which is usually called free cutting steel.

6. Chromium (CR): in structural steel and tool steel, chromium can significantly improve the strength, hardness and wear resistance, but at the same time reduce the plasticity and toughness. Chromium can improve the oxidation resistance and corrosion resistance of steel, so it is an important alloy element of stainless steel and heat-resistant steel.

7. Nickel (Ni): nickel can improve the strength of steel while maintaining good plasticity and toughness. Nickel has high corrosion resistance to acid and alkali, rust and heat resistance at high temperature. However, as nickel is a scarce resource, other alloy elements should be used instead of nickel chromium steel.

8. Molybdenum (MO): molybdenum can refine the grains of steel, improve hardenability and thermal strength, and maintain sufficient strength and creep resistance at high temperature (long-term stress at high temperature, deformation, called creep). Adding molybdenum to structural steel can improve mechanical properties. The brittleness of alloy steel caused by fire can also be restrained. Redness can be improved in tool steel.

9. Titanium (TI): titanium is a strong deoxidizer in steel. It can make the internal structure of steel compact, refine the grain strength, reduce the aging sensitivity and cold brittleness. Improve welding performance. Intergranular corrosion can be avoided by adding proper titanium to CR 18 Ni 9 austenitic stainless steel.

10. Vanadium (V): vanadium is a good deoxidizer for steel. Adding 0.5% vanadium to the steel can refine the structure grain and improve the strength and toughness. The carbide formed by vanadium and carbon can improve the hydrogen corrosion resistance under high temperature and pressure.

11. Tungsten (W): tungsten has a high melting point and a large ratio. It is a noble alloy element. Tungsten carbide formed by tungsten and carbon has high hardness and wear resistance. When tungsten is added to tool steel, the red hardness and heat strength can be significantly improved, which can be used as cutting tools and forging dies.

12. NB: NB can refine grain, reduce overheat sensitivity and temper brittleness of steel, increase strength, but decrease plasticity and toughness. Adding niobium to ordinary low alloy steel can improve the resistance to atmospheric corrosion and hydrogen, nitrogen and ammonia corrosion at high temperature. Niobium can improve welding performance. Adding niobium to austenitic stainless steel can prevent intergranular corrosion.

13. Cobalt (CO): cobalt is a rare and precious metal, which is often used in special steels and alloys, such as hot steel and magnetic materials.

14. Copper (Cu): steel made from Daye ore at WISCO, often containing copper. Copper can improve strength and toughness, especially atmospheric corrosion. The disadvantage is that it is easy to produce hot embrittlement during hot working, and the plasticity of copper content more than 0.5% is significantly reduced. When the copper content is less than 0.50%, there is no effect on weldability.

15. Aluminum (AL): aluminum is a commonly used deoxidizer in steel. Adding a small amount of aluminum into the steel can refine the grain and improve the impact toughness, such as 08Al steel for deep drawing sheet. Aluminum also has anti-oxidation and anti-corrosion properties. When used together with chromium and silicon, aluminum can significantly improve the high-temperature peeling resistance and high-temperature corrosion resistance of steel. The disadvantage of aluminum is that it affects the hot working performance, welding performance and cutting performance of steel.

16. Boron (b): adding a small amount of boron to the steel can improve the compactness, hot rolling performance and strength of the steel.

17. Nitrogen (n): nitrogen can improve the strength, low temperature toughness and weldability of steel, and increase the aging sensitivity.

18. Rare earth (XT): rare earth elements refer to 15 lanthanide elements with atomic numbers of 57-71 in the periodic table of elements. These elements are all metals, but their oxides are very similar to "Earth", so they are often called rare earth. The composition and shape of inclusions in steel can be changed by adding rare earth.