The main role of alloying elements in steel pipes
1. Carbon (C): The carbon content in the steel increases, the yield point and tensile strength increase, but the plasticity and impact resistance decrease. When the carbon content exceeds 0.23%, the weldability of the steel deteriorates, so it is used for welding. For low-alloy structural steels, the carbon content generally does not exceed 0.20%. High carbon content also reduces the atmospheric corrosion resistance of steel. High carbon steel in the open yard is susceptible to corrosion; in addition, carbon can increase the cold brittleness and age sensitivity of steel.
2. Silicon (Si): Silicon is added as a reducing agent and a deoxidizer during the steel making process, so the killed steel contains 0.15-0.30% of silicon. If the silicon content in the steel exceeds 0.50-0.60%, silicon is an alloying element. Silicon can significantly improve the elastic limit of steel, yield point and tensile strength, so it is widely used as spring steel. Adding 1.0-1.2% silicon to the quenched and tempered structural steel increases the strength by 15-20%. Silicon and molybdenum, tungsten, chromium and other knots
It can improve the corrosion resistance and oxidation resistance and can manufacture heat resistant steel. Silicon-containing 1-4% low carbon steel, with a very high magnetic permeability, used in the electrical industry to make silicon steel sheet. An increase in the amount of silicon will reduce the weldability of the steel.
3. Manganese (Mn): In the process of steel making, manganese is a good deoxidizer and desulfurizer. Generally, steel contains 0.30-0.50% manganese. When adding more than 0.70% of carbon steel, even if it is "manganese steel", it has more toughness than ordinary steel, and has higher strength and hardness, improves the quenchability of steel, and improves the hot workability of steel. For example, 16Mn steel is 40% higher than the A3 yield point. 11-14% manganese containing steel has extremely high wear resistance, used in excavator buckets, ball mill liners, etc. The increase in the amount of manganese reduces the corrosion resistance of the steel and reduces the welding performance.
4. Phosphorus (P): Under normal circumstances, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, deteriorates the welding performance, reduces the plasticity, and deteriorates the cold bending performance. Therefore, it is usually required that the phosphorus content in the steel is less than 0.045%, and the demand for high-quality steel is lower.
5. Sulfur (S): Sulfur is also a harmful element under normal conditions. The steel is made to be hot brittle, reduce the ductility and toughness of the steel, and cause cracks during forging and rolling. Sulfur is also detrimental to weldability and reduces corrosion resistance. Therefore, the sulfur content is usually required to be less than 0.055%, and the high-quality steel is required to be less than 0.040%. The addition of 0.08-0.20% sulfur to the steel improves the machinability and is commonly referred to as free-cutting steel.
6. Chromium (Cr): In structural steel and tool steel, chromium can significantly improve strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium can improve the oxidation resistance and corrosion resistance of steel, and is therefore an important alloying element for stainless steel and heat-resistant steel.
7. Nickel (Ni): Nickel can increase the strength of steel while maintaining good ductility and toughness. Nickel has high corrosion resistance to acids and bases, and has rust and heat resistance at high temperatures. However, since nickel is a scarce resource, other alloying elements should be used instead of nickel-chromium steel.
8. Molybdenum (Mo): Molybdenum can refine the grain of steel, improve hardenability and heat strength, and maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperature, deformation occurs, weigh Creep). The addition of molybdenum to the structural steel improves mechanical properties. It is also possible to suppress the brittleness of the alloy steel due to fire. 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 dense, refine grain force; reduce aging sensitivity and cold brittleness. Improve welding performance. The addition of appropriate titanium to the chromium 18 nickel 9 austenitic stainless steel avoids intergranular corrosion.
10. Vanadium (V): Vanadium is an excellent deoxidizer for steel. Adding 0.5% vanadium to the steel refines the grain of the structure and improves strength and toughness. Carbides formed from vanadium and carbon improve hydrogen corrosion resistance at high temperatures and pressures.
11. Tungsten (W): Tungsten has a high melting point and a large specific gravity. It is an alloying element of precious earth. Tungsten and carbon form tungsten carbide with high hardness and wear resistance. Adding tungsten to tool steel can significantly improve red hardness and heat strength for cutting tools and forging dies.
12. Niobium (Nb): niobium can refine grains and reduce the superheat sensitivity and temper brittleness of steel, improve strength, but decrease plasticity and toughness. The addition of bismuth in ordinary low-alloy steel can improve the resistance to atmospheric corrosion and hydrogen, nitrogen and ammonia corrosion at high temperatures.铌 can improve the welding performance. Twisting in austenitic stainless steel prevents intergranular corrosion.
2. Silicon (Si): Silicon is added as a reducing agent and a deoxidizer during the steel making process, so the killed steel contains 0.15-0.30% of silicon. If the silicon content in the steel exceeds 0.50-0.60%, silicon is an alloying element. Silicon can significantly improve the elastic limit of steel, yield point and tensile strength, so it is widely used as spring steel. Adding 1.0-1.2% silicon to the quenched and tempered structural steel increases the strength by 15-20%. Silicon and molybdenum, tungsten, chromium and other knots
It can improve the corrosion resistance and oxidation resistance and can manufacture heat resistant steel. Silicon-containing 1-4% low carbon steel, with a very high magnetic permeability, used in the electrical industry to make silicon steel sheet. An increase in the amount of silicon will reduce the weldability of the steel.
3. Manganese (Mn): In the process of steel making, manganese is a good deoxidizer and desulfurizer. Generally, steel contains 0.30-0.50% manganese. When adding more than 0.70% of carbon steel, even if it is "manganese steel", it has more toughness than ordinary steel, and has higher strength and hardness, improves the quenchability of steel, and improves the hot workability of steel. For example, 16Mn steel is 40% higher than the A3 yield point. 11-14% manganese containing steel has extremely high wear resistance, used in excavator buckets, ball mill liners, etc. The increase in the amount of manganese reduces the corrosion resistance of the steel and reduces the welding performance.
4. Phosphorus (P): Under normal circumstances, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, deteriorates the welding performance, reduces the plasticity, and deteriorates the cold bending performance. Therefore, it is usually required that the phosphorus content in the steel is less than 0.045%, and the demand for high-quality steel is lower.
5. Sulfur (S): Sulfur is also a harmful element under normal conditions. The steel is made to be hot brittle, reduce the ductility and toughness of the steel, and cause cracks during forging and rolling. Sulfur is also detrimental to weldability and reduces corrosion resistance. Therefore, the sulfur content is usually required to be less than 0.055%, and the high-quality steel is required to be less than 0.040%. The addition of 0.08-0.20% sulfur to the steel improves the machinability and is commonly referred to as free-cutting steel.
6. Chromium (Cr): In structural steel and tool steel, chromium can significantly improve strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium can improve the oxidation resistance and corrosion resistance of steel, and is therefore an important alloying element for stainless steel and heat-resistant steel.
7. Nickel (Ni): Nickel can increase the strength of steel while maintaining good ductility and toughness. Nickel has high corrosion resistance to acids and bases, and has rust and heat resistance at high temperatures. However, since nickel is a scarce resource, other alloying elements should be used instead of nickel-chromium steel.
8. Molybdenum (Mo): Molybdenum can refine the grain of steel, improve hardenability and heat strength, and maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperature, deformation occurs, weigh Creep). The addition of molybdenum to the structural steel improves mechanical properties. It is also possible to suppress the brittleness of the alloy steel due to fire. 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 dense, refine grain force; reduce aging sensitivity and cold brittleness. Improve welding performance. The addition of appropriate titanium to the chromium 18 nickel 9 austenitic stainless steel avoids intergranular corrosion.
10. Vanadium (V): Vanadium is an excellent deoxidizer for steel. Adding 0.5% vanadium to the steel refines the grain of the structure and improves strength and toughness. Carbides formed from vanadium and carbon improve hydrogen corrosion resistance at high temperatures and pressures.
11. Tungsten (W): Tungsten has a high melting point and a large specific gravity. It is an alloying element of precious earth. Tungsten and carbon form tungsten carbide with high hardness and wear resistance. Adding tungsten to tool steel can significantly improve red hardness and heat strength for cutting tools and forging dies.
12. Niobium (Nb): niobium can refine grains and reduce the superheat sensitivity and temper brittleness of steel, improve strength, but decrease plasticity and toughness. The addition of bismuth in ordinary low-alloy steel can improve the resistance to atmospheric corrosion and hydrogen, nitrogen and ammonia corrosion at high temperatures.铌 can improve the welding performance. Twisting in austenitic stainless steel prevents intergranular corrosion.
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