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The effect of alloying elements on the properties of steel

The effect of alloying elements on the properties of steel

1. C

When the carbon content of steel increases, the yield point and tensile strength increase, but the plasticity and impact decrease. When the carbon content of steel exceeds 0.23%, the welding performance of steel becomes worse. Therefore, the carbon content of low-alloy structural steel used for welding generally does not exceed 0.20%.High carbon content will also reduce the atmospheric corrosion resistance of steel, 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. Si

Adding silicon as reducing agent and deoxidizer in the process of steel making, the composed steel contains 0.15-0.30% silicon.If the silicon content of steel exceeds 0.50-0.60%, silicon is considered as alloying 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 improve the strength by 15-20%.The combination of silicon and molybdenum, tungsten, chromium, etc. can improve the corrosion resistance and oxidation resistance, can produce heat resistant steel.Silicon 1-4% low carbon steel, with a very high magnetic conductivity, used in the electrical industry to make silicon steel sheet.The increase of silicon will reduce the welding performance of steel.

3. Mn

In the process of steelmaking, manganese is a good deoxidizer and desulfurizer,general steel contains manganese 0.30-0.50%.When more than 0.70% of carbon steel is added, it is considered as "manganese steel". Compared with general steel, the steel not only has enough toughness, but also has higher strength and hardness, so as to improve the hardenability of steel and the thermal processing performance of steel.For example, 16Mn steel is 40% higher than A3 yield point.Manganese 11-14% steel has very high wear resistance, used in excavators, shovels, ball mill liner, etc.The increase of manganese reduces the corrosion resistance and welding performance of steel.

4. P

In general, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, makes the welding performance worse, reduces the plasticity, and makes the cold bending performance worse.Therefore, it is usually required that the phosphorus content in steel is less than 0.045%.

5. S

Sulfur is also a harmful element in general.It causes hot brittleness of steel, reduces its ductility and toughness, and causes cracks during forging and rolling.Sulfur is also detrimental to welding properties, reducing corrosion resistance.Therefore, the sulfur content is usually less than 0.055%, and the quality of steel is less than 0.04%.Adding 0.08%-0.2% sulfur to steel can improve machinability. It is usually called free-cutting steel.

6. 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. 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. Mo

Molybdenum can refine the grains of steel, improve the 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. 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. 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. W

Tungsten is a noble alloy element with high melting point and high ratio. 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

Niobium can refine grains, reduce superheat sensitivity and temper brittleness of steel, increase strength, but plasticity and toughness decrease. 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. Co

Cobalt is a rare precious metal, which is often used in special steels and alloys, such as hot steel and magnetic materials.

14. Cu

The steel made from Daye ore in WISCO often contains 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. 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 oxidation resistance and corrosion resistance. When aluminum is used together with chromium and silicon, it 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. B

The compactness, hot rolling property and strength of the steel can be improved by adding a small amount of boron into the steel.

17. N

Nitrogen can improve the strength, low temperature toughness and weldability of steel, and increase the aging sensitivity.

18. 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 addition of re to steel can change the composition, shape, distribution and properties of inclusions in steel, thus improving various properties of steel, such as toughness, weldability and cold working performance. Adding rare earth to plowshare steel can improve wear resistance.

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