Steel is an alloy of iron, carbon and a small amount of other elements. For steel, different elements affect the properties of steel in different ways. Today, Cheng Cheng Xiaobian will talk about the influence of various elements on the properties of steel. properties of steel and mechanism.
Carbon element (C): Carbon is the most important element that determines the characteristics of steel. Increasing the carbon content of steel will increase the yield strength and tensile strength, but the ductility and toughness will decrease when the carbon content exceeds 0.23%. At the same time, the welding characteristics of steel also deteriorate, so the carbon content in low-alloy structural steel used for welding, as a rule, cannot exceed 0.20%. The high carbon content also reduces the atmospheric corrosion resistance of steel. For example, high-carbon steel in outdoor warehouses is particularly susceptible to corrosion; in addition, carbon can increase the cold brittleness and aging sensitivity of steel, as well as control the carbon content. in real production, the amount of steel has a great influence on the productivity of the steel produced.
Silicon (Si): Silicon is added as a reducing agent and deoxidizing agent during the steel making process, so normally 0.15~0.30% silicon is contained in the quiet steel. If the silicon content of the steel exceeds 0.50~0.60%, silicon is considered an alloying element. Silicon can greatly improve the elastic strength, yield strength and tensile strength of steel, so it is widely used to make spring steel. Adding 1.0~1.2% silicon to quenched and tempered structural steel can increase strength by 15~20%.
Combining silicon with molybdenum, tungsten, chromium, etc. can improve corrosion resistance and oxidation resistance, and make heat resistant steel. Low carbon steel containing 1-4% silicon has an extremely high magnetic permeability, so it is often used in the electrical industry to make silicon steel sheets. In welding, an increase in the silicon content reduces the weldability of the steel. It can be said that the control of silicon content will affect the applications and steel scenarios.
Manganese Element (Mn): In the process of steel production, manganese is a good deoxidizer and desulfurizer, and usually steel contains 0.30~1.00% manganese. When more than 0.70% is added to carbon steel, it is considered "manganese steel". Compared with steel with a total manganese content, it not only has sufficient toughness, but also has higher strength and hardness, which improves the steel's hardenability and improves hot workability. steel, for example, the yield strength of 16Mn steel is 40% higher than that of A3 steel. Steel containing 11-14% manganese has extremely high wear resistance and is used for making excavator buckets, lining of ball mills, etc. In addition, with an increase in manganese content, the corrosion resistance of steel weakens and welding productivity decreases.
Phosphorus (P), Sulfur (S): Generally, Phosphorus (P) and Sulfur (S) are harmful elements in steel, and increasing their content reduces ductility, toughness, welding performance, etc. In the actual production, the content of the two elements must be controlled. Generally, the P content is required not to exceed 0.045% and the S content not to exceed 0.050%. The lower the content, the better the performance of the steel. .
Chromium (Cr): In structural and tool steel, chromium can greatly increase strength, hardness and wear resistance, but at the same time reduce ductility and toughness. Chromium can improve the oxidation resistance and corrosion resistance of steel, so it is an important alloying element for stainless steel and high temperature steel.
Nickel element (Ni): Nickel can increase the strength of steel while maintaining good ductility and toughness. Nickel has high corrosion resistance to acid and alkali, as well as anti-corrosion and heat resistance at high temperatures, so it is also an important alloying element in many stainless and high temperature steels.
Molybdenum (Mo): Molybdenum can refine steel grains, improve hardenability and thermal strength, and maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperatures, deformation called creep). Adding molybdenum to structural steel can improve the mechanical properties. In addition, the Mo element can also reduce the brittleness of alloy steel caused by quenching. In tool steel, the element Mo can improve the hardness redness (refers to the ability of a material to maintain its hardness after holding at a certain temperature for a certain period of time).
Titanium (Ti): Titanium is a strong deoxidizing agent in steel. It can make the internal structure of steel dense, improve grain strength, reduce aging susceptibility and cold brittleness. Improve welding quality. Adding Appropriate Titanium to Cr18N Austenitic Stainless Steeli9 avoids intergranular corrosion.
Vanadium (V): Vanadium is an excellent deoxidizer for steel. Adding about 0.5% vanadium to steel can reduce the graininess of the structure and improve strength and toughness. The carbide formed by vanadium and carbon can improve the hydrogen corrosion resistance at high temperature and high pressure.
Tungsten Element (W): Tungsten has a high melting point and high specificity, and is also a precious alloy element. Tungsten and carbon form tungsten carbide, which has high hardness and wear resistance. The addition of tungsten to tool steel can greatly improve red hardness and thermal strength, and is commonly used for cutting tool steel (high speed steel) and die steel for forging.
The element niobium (Nb): it can refine grain and reduce steel's overheating sensitivity and temper brittleness, and increase strength, but ductility and toughness are reduced. The addition of niobium to ordinary low alloy steel can improve the resistance to atmospheric corrosion, as well as the resistance to hydrogen, nitrogen and ammonia corrosion at high temperatures. In addition, adding niobium to austenitic stainless steel can prevent intergranular corrosion.
Cobalt (Co): It is mainly used in special steels and alloys such as high temperature steels and magnetic materials to improve the oxidation resistance of high temperature steels and enhance the magnetic saturation properties of magnetic materials.
Copper element (Cu): can improve the atmospheric corrosion resistance of steel. If the copper content of the steel exceeds 0.75%, by solid solution treatment and aging, the effect of precipitation hardening can be achieved, and the strength of the steel can be greatly improved.
Aluminum element (Al): Aluminum is a widely used deoxidizer in steel. Adding a small amount of aluminum to steel can reduce grain size and improve toughness. Aluminum also has anti-oxidation and anti-corrosion properties. The combination of aluminum, chromium and silicon can greatly improve the resistance of steel to high temperature oxidation and high temperature corrosion. The disadvantage of aluminum is that it affects the hot workability, welding and cutting characteristics of the steel.
Boron element (B): Adding a small amount of boron to steel can improve the density and hot rolling characteristics of steel, and increase strength and hardenability.
Nitrogen (N). Nitrogen can improve the strength, low temperature toughness and weldability of steel, and increase aging sensitivity.
The quality and performance of steel is determined by the need.Different needs require different content of elements. In the production and application of steel, understanding the influence of various elements on the properties of steel can effectively control quality and guide the choice of materials. Understanding this knowledge will give twice the result with half the effort in production work. .