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Steel pipe material composition knowledge

Oct 26, 2017

Interpretation of chemical composition

1, carbon (C): increased carbon content in steel, yield points and tensile strength increased, but the plasticity and impact reduction, when the carbon 0.23% over, the steel welding performance deterioration, so for welding Low alloy structural steel, carbon content is generally not more than 0.20%. The high carbon content also reduces the atmospheric corrosion resistance of steel, and the high carbon steel in the open field is easy to rust. In addition, carbon can increase the cold brittleness and aging sensitivity of steel.

2, silicon (Si): in the steelmaking process as a reducing agent and deoxidizer, so sedative steel containing 0.15-0.30% of the silicon. If the silicon content of steel exceeds 0.50-0.60%, silicon even alloying elements. Silicon can significantly improve the elastic limit of steel, yield point and tensile strength, it is widely used for spring steel. In the quenched and tempered structural steel by adding 1.0-1.2% of the silicon, the strength can be increased by 15-20%. Silicon and molybdenum, tungsten, chromium and other combinations, to improve the role of corrosion resistance and oxidation, can produce heat-resistant steel. Silicon-containing 1-4% of low-carbon steel, with a high permeability, for the electrical industry to do silicon steel. Increasing the amount of silicon will reduce the weldability of the steel.

3, manganese (Mn): In the steelmaking process, manganese is a good deoxidizer and desulfurization agent, the general steel containing 0.30-0.50% manganese. When adding 0.70% or more of carbon steel, it will not only have sufficient toughness, but also have high strength and hardness, improve the quenching of steel and improve the hot working performance of steel even if it is "manganese steel" Such as 16Mn steel than A3 yield point 40% higher. Containing 11-14% of the steel has a high wear resistance, for the excavator bucket, ball mill liner. Manganese increased, reducing the corrosion resistance of steel, reducing welding performance.

4, phosphorus (P): In general, phosphorus is a harmful element in steel, increasing the cold brittle steel, so that deterioration of welding performance, reduce plasticity, so that cold bending performance deterioration. Therefore, the amount of phosphorus in the steel is usually less than 0.045%, high-quality steel requirements lower.

5, sulfur (S): sulfur in the usual case is harmful elements. So that the hot brittle steel, steel to reduce the ductility and toughness, in the forging and rolling caused by cracks. Sulfur on the welding performance is also unfavorable, reduce corrosion resistance. So usually require less than 0.055% sulfur content, high-quality steel requirements of less than 0.040%. Adding 0.08-0.20% sulfur to the steel can improve machinability, often 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, which is an important alloy of stainless steel, heat-resistant steel.

7, nickel (Ni): nickel can improve the strength of steel, but to maintain good plasticity and toughness. Nickel has a high corrosion resistance to acid and alkali, rust and heat resistance at high temperatures. However, because nickel is a scarce resource, it should try to use other alloy elements instead of nickel-chromium steel.

8, molybdenum (Mo): molybdenum can make steel grain refinement, improve the hardenability and thermal strength, at high temperatures to maintain sufficient strength and creep resistance (long-term stress at high temperatures, deformation Creep). Structural steel by adding molybdenum, can improve the mechanical properties. It is also possible to suppress the brittleness of the alloy steel due to the fire. In the tool steel can improve the red.

9, titanium (Ti): titanium is a strong deoxidizer in steel. It can make the internal structure of steel dense, fine grain strength; reduce aging sensitivity and cold brittleness. Improve welding performance. In the chrome 18 nickel 9 austenitic stainless steel by adding the appropriate titanium, to avoid intergranular corrosion.

10, vanadium (V): vanadium is an excellent deoxidizer for steel. Adding 0.5% of the steel in the steel can refine the grain, improve strength and toughness. Vanadium and carbon carbide, in high temperature and high pressure can improve the ability of hydrogen corrosion.

11, tungsten (W): tungsten melting point is high, the proportion of large, is the precious alloy elements. Tungsten and carbon to form tungsten carbide has a high hardness and wear resistance. In the tool steel plus tungsten, can significantly improve the red hardness and thermal strength, for cutting tools and forging die.

12, niobium (Nb): niobium can refine the grain and reduce the steel overheating sensitivity and temper brittleness, improve the strength, but the plasticity and toughness decreased. In the ordinary low-alloy steel niobium, can improve the anti-atmospheric corrosion and high temperature hydrogen, nitrogen, ammonia corrosion capacity. Niobium improves weldability. Adding niobium to austenitic stainless steel prevents intergranular corrosion.

13, cobalt (Co): cobalt is a rare precious metal, used for special steel and alloys, such as hot steel and magnetic materials.

14, copper (Cu): Wuhan Iron and Steel with Daye ore refining the steel, often containing copper. Copper can improve strength and toughness, especially atmospheric corrosion performance. The disadvantage is that in the hot processing is easy to produce hot brittle, copper content of more than 0.5% plastic significantly reduced. When the copper content is less than 0.50% has no effect on the weldability.

15, aluminum (Al): aluminum is commonly used in steel deoxidizer. Steel to add a small amount of aluminum, can refine the grain, improve the impact toughness, such as deep drawing plate 08Al steel. Aluminum also has antioxidant and corrosion resistance, aluminum and chromium, silicon combined, can significantly improve the high temperature of steel can not afford the performance and high temperature corrosion resistance. The disadvantage of aluminum is the impact of steel thermal processing performance, welding performance and cutting performance.

16, boron (B): steel by adding trace amounts of boron can improve the steel's compactness and hot-rolled properties, improve strength.

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

18, rare earth (Xt): rare earth elements of the periodic table is the atomic number of 57-71 15 lanthanides. These elements are metal, but their oxides are like "soil", so it is customary to say rare earth. The addition of rare earth to the steel can alter the composition, morphology, distribution and properties of the inclusions in the steel, thereby improving the performance of the steel, such as toughness, weldability, and cold workability. In the plowing steel by adding rare earth, can improve wear resistance.