Effect of chemical elements on steel properties

Effect of chemical elements on steel properties

2019-07-27 10:55:26 68

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 combined with molybdenum, tungsten, chromium, etc., has the effect of improving 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.


13. Cobalt (Co): Cobalt is a rare precious metal used in special steels and alloys such as heat-strength steel and magnetic materials.


14. Copper (Cu): Steel produced by WISCO with Daye ore often contains copper. Copper improves strength and toughness, especially atmospheric corrosion. The disadvantage is that it is prone to hot brittleness during hot working, and the copper content is significantly reduced by more than 0.5%. When the copper content is less than 0.50%, there is no influence on the weldability.


15. Aluminum (Al): Aluminum is a commonly used deoxidizer in steel. A small amount of aluminum is added to the steel to refine the grains and improve the impact toughness, such as 08Al steel for deep-drawing thin sheets. Aluminum also has oxidation resistance and corrosion resistance. Aluminum is combined with chromium and silicon to significantly improve the high temperature and corrosion resistance of steel. The disadvantage of aluminum is that it affects the hot workability, weldability and machinability of steel.


16. Boron (B): Adding a trace amount of boron to the steel can improve the compactness and hot rolling properties of the steel and increase the strength.


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


18. Rare Earth (Xt): Rare earth element refers to 15 lanthanides with an atomic number of 57-71 in the periodic table. These elements are all metals, but their oxides are very similar to "earth", so they are used to called rare earths. The addition of rare earths in steel can change the composition, morphology, distribution and properties of inclusions in the steel, thereby improving various properties of the steel, such as toughness, weldability, and cold workability. Adding rare earth to the plough steel can improve wear resistance.