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1. Carbon (C): The yield point and tensile strength of steel increase with the increase of carbon content, but the plasticity and impact properties decrease. When carbon content exceeds 0.23%, the weldability of steel deteriorates. Therefore, the carbon content of low alloy structural steel used for welding generally does not exceed 0.20%. High carbon content also reduces the atmospheric corrosion resistance of steel, which is easy to rust in open yard. In addition, carbon can increase the cold brittleness and aging sensitivity of steel.
2. Silicon (Si): Silicon is added as reducing agent and deoxidizing agent in steelmaking process, so killed steel contains 0.15-0.30% silicon. If the content of silicon in steel exceeds 0.50-0.60%, silicon is an alloy element. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, so it is widely used as spring steel. By adding 1.0-1.2% silicon to tempered structural steel, the strength can be increased by 15-20%. Silicon and Molybdenum, Tungsten and Chromium Junctions
It has the function of improving corrosion resistance and oxidation resistance, and can make heat-resistant steel. Low carbon steel containing 1-4% silicon has very high permeability, which is used for making silicon steel sheets in electrical industry. The increase of silicon content will reduce the weldability of steel.
3. Manganese (Mn): Manganese is a good deoxidizer and desulfurizer in steelmaking process, and generally contains 0.30-0.50% manganese in steel. When more than 0.70% of the carbon steel is added, the "manganese steel" has not only enough toughness, but also higher strength and hardness than the ordinary steel. It can improve the hardenability and hot working performance of the steel, such as 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. It is used for shovel of excavator, lining plate of ball mill, etc. Increasing manganese content weakens corrosion resistance and weldability of steel.
4. Phosphorus (P): In general, phosphorus is a harmful element in steel. It increases the cold brittleness of steel, deteriorates the weldability, reduces the plasticity and deteriorates the cold bending performance. Therefore, the phosphorus content in steel is usually required to be less than 0.045%, and the requirement for high quality steel is lower.
5. Sulphur (S): Sulphur is also a harmful element under normal circumstances. It causes hot brittleness of steel, reduces ductility and toughness of steel, and causes cracks during forging and rolling. Sulphur is also harmful to weldability and reduces corrosion resistance. So the sulfur content is usually less than 0.055% and the quality steel is less than 0.040%. Adding 0.08-0.20% sulphur in steel can improve the machinability, which is usually called free-cutting steel.
6. Chromium (Cr): In structural and tool steels, chromium can significantly improve strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium can also 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 and maintain good plasticity and toughness. Nickel has high corrosion resistance to acid and alkali, rust resistance and heat resistance at high temperature. However, because nickel is a scarce resource, other alloy elements should be used instead of nickel-chromium steel as far as possible.
8. Molybdenum (Mo): Molybdenum can refine the grain size 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). The mechanical properties of structural steel can be improved by adding molybdenum. It can also inhibit the brittleness of alloy steel caused by fire. The 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 grain strength, reduce aging sensitivity and cold brittleness. Improve welding performance. Intergranular corrosion can be avoided by adding appropriate titanium to austenitic stainless steel chromium 18Ni 9.
10. Vanadium (V): Vanadium is an excellent deoxidizer for steel. The addition of 0.5% vanadium in steel can refine the grain structure and improve the strength and toughness. The carbide formed by vanadium and carbon can improve the hydrogen corrosion resistance at high temperature and high pressure.
11. Tungsten (W): Tungsten has a high melting point and a high specific gravity. It is a precious alloy element. Tungsten carbide formed from tungsten and carbon has high hardness and wear resistance. When tungsten is added to tool steel, the red hardness and thermal strength can be significantly improved, and it can be used as cutting tool and forging die.
Niobium (Nb): Niobium can refine grain size, reduce superheat sensitivity and temper brittleness of steel, increase strength, but decrease plasticity and toughness. The addition of Nb in common low alloy steel can improve the resistance to atmospheric corrosion and hydrogen, nitrogen and ammonia corrosion at high temperature. Niobium can improve welding performance. The intergranular corrosion can be prevented by adding Nb in austenitic stainless steel.
13. Cobalt (Co): Cobalt is a rare precious metal, which is often used in special steels and alloys, such as Hot-Strength steels and magnetic materials.
14. Copper (Cu): Steel made from Daye ore of WISCO often contains copper. Copper can improve strength and toughness, especially atmospheric corrosion. The disadvantage is that hot brittleness easily occurs during hot working, and the plasticity of copper content more than 0.5% decreases significantly. When the copper content is less than 0.50%, it has no effect on the weldability.
15. Aluminum (Al): Aluminum is a common deoxidant in steel. Adding a small amount of aluminium in steel can refine grain size and improve impact toughness, such as 08Al steel for deep drawing sheet. Aluminum also has antioxidant and corrosion resistance. The combination of aluminium with chromium and silicon can significantly improve the high temperature peeling resistance and high temperature corrosion resistance of steel. The disadvantage of aluminium is that it affects the hot working, welding and cutting properties of steel.
16. Boron (B): The compactness, hot rolling properties and strength of steel can be improved by adding trace boron.
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 lanthanides with atomic number 57-71 in the periodic table of elements. These elements are all metals, but their oxides are much like "earth", so they are customarily called rare earths. The composition and shape of inclusions in steel can be changed by adding rare earth into steel.