October 20, 2022
introduce
The main alloying elements of alloy steel are silicon, manganese, chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, aluminum, copper, boron, rare earth, etc.
Vanadium, titanium, niobium and zirconium are strong carbide forming elements in steel. As long as there is enough carbon, their carbides can be formed under appropriate conditions. When carbon is absent or under high temperature conditions, they enter the solid solution in an atomic state. Manganese, chromium, tungsten and molybdenum are carbide forming elements, some of which enter the solid solution in atomic state, and the other part forms displacement alloy cementite. Aluminum, copper, nickel, cobalt and silicon are elements that do not form carbides and generally exist in the atomic state in solid solutions.
role
Alloy structural steel
Alloy structural steel
1, carbon (C) : steel carbon content increases, yield point and tensile strength increases, but plasticity and impact decreased, when the carbon content exceeds 0.23%, steel welding performance deteriorated, so used for welding of low alloy structural steel, carbon content generally does not exceed 0.20%. High carbon content will also reduce the atmospheric corrosion resistance of steel, high carbon steel in the open field is easy to rust; In addition, carbon can increase cold brittleness and age sensitivity of steel.
2, silicon (Si) : silicon is added as a reducing agent and deoxidizer in the process of steel making, so the steel contains 0.15-0.30% silicon. Silicon is considered an alloying element if the steel contains more than 0.50 to 0.60% silicon. Silicon can significantly increase 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 quenched and tempered structural steel can increase the strength by 15-20%. The combination OF SILICON and molybdenum, tungsten, chromium, etc., has the effect of improving corrosion resistance and oxidation resistance, and can make heat resistant steel. Low carbon steel CONTAINING 1-4% silicon, with very high magnetic conductivity, used in electrical industry as silicon steel sheet. The increase of silicon will reduce the welding performance of steel.
3, manganese (Mn) : in the process of steelmaking, manganese is a good deoxidizer and desulfurizer, the general steel containing manganese 0.30-0.50%. When the carbon steel is added more than 0.70%, even if the "manganese steel", the steel of the general amount of steel not only has enough toughness, but also has higher strength and hardness, improve the quenchability of steel, improve the hot working performance of steel, such as 16Mn steel is 40% higher than A3 yield point. Manganese 11-14% STEEL with very HIGH wear resistance, used for excavator bucket, ball mill LINings, etc. The increase of manganese will weaken the corrosion resistance of steel and reduce the welding performance.
4, phosphorus (P) : in general, phosphorus is a harmful element in steel, increase the cold brittleness of steel, make the welding performance bad, reduce plasticity, make the cold bending performance bad. Therefore, phosphorus content in steel is usually required to be less than 0.045%, and high quality steel is required to be lower.
5, sulfur (S) : sulfur is usually a harmful element. It makes the steel hot brittle, reduces the ductility and toughness of the steel, and causes cracks during forging and rolling. Sulfur is also detrimental to welding performance and reduces corrosion resistance. Therefore, sulfur content is usually required to be less than 0.055%, and high quality steel is required to be less than 0.040%. Adding 0.08-0.20% sulfur to steel can improve the machinability, usually 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 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, nickel (Ni) : nickel can improve the strength of steel, and maintain good plasticity and toughness. Nickel has high corrosion resistance to acid and alkali, rust resistance and heat resistance at high temperature. However, as nickel is a scarce resource, other alloying elements should be used instead of nickel chromium steel.
8, molybdenum (Mo) : molybdenum can make steel grain refinement, improve hardenability and thermal strength performance, at high temperature to maintain sufficient strength and anti-creep ability (long-term stress at high temperature, deformation, called creep). The mechanical properties of structural steel can be improved by adding molybdenum. It can also restrain the brittleness of alloy steel caused by quenching. Redness can be improved in tool steel.
9, titanium (Ti) : titanium is a strong deoxidizer in steel. It can make the inner structure of steel compact and refine the grain force; Reduce time sensitivity and cold brittleness. Improve welding performance. Intergranular corrosion can be avoided by adding appropriate titanium to Cr 18 Ni 9 austenitic stainless steel.
10, vanadium (V) : vanadium is an excellent deoxidizer of steel. Adding 0.5% vanadium to steel can refine microstructure grain, improve strength and toughness. The carbides formed by vanadium and carbon can improve the resistance to hydrogen corrosion under high temperature and pressure.
11, tungsten (W) : tungsten melting point is high, than the major, is a rare alloy element. Tungsten carbide formed from tungsten and carbon has high hardness and wear resistance. Adding tungsten to tool steel can significantly improve the red rigidity and thermal strength, which can be used as cutting tools and forging dies.
12, niobium (Nb) : Niobium can refine the grain and reduce the overheating sensitivity and tempering brittleness of steel, improve the strength, but plasticity and toughness decreased. Adding niobium to ordinary low alloy steel can improve the resistance to atmospheric corrosion and to hydrogen, nitrogen and ammonia corrosion at high temperature. Niobium can improve welding performance. Intergranular corrosion can be prevented by adding niobium to austenitic stainless steel.
13, cobalt (Co) : Cobalt is a rare precious metal, mostly used in special steel and alloy, such as hot steel and magnetic materials.
14, copper (Cu) : Wuhan Iron and steel with Daye ore smelting steel, often contains copper. Copper can improve strength and toughness, especially for atmospheric corrosion. The disadvantage is that it is easy to produce hot embrittlement during hot machining, and the plasticity is significantly reduced when the copper content exceeds 0.5%. When the copper content is less than 0.50%, it has no effect on weldability.
15, aluminum (Al) : Aluminum is a commonly used deoxidizer in steel. Adding a small amount of aluminum in 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. Aluminum combined with chromium and silicon can significantly improve the high temperature anti-peeling performance and high temperature corrosion resistance of steel. The disadvantage of aluminum is that it affects the hot working, welding and cutting properties of steel.
16, boron (B) : adding a trace amount of boron to steel can improve the densification and hot rolling properties of steel, improve the strength.
17, nitrogen (N): nitrogen can improve the strength of steel, low temperature toughness and weldability, increase aging sensitivity.
18. Rare earth (Xt) : rare earth elements refer to 15 lanthanides with atomic numbers of 57-71 in the periodic table of elements. These elements are all metals, but their oxides look like earth, so they are called rare earths. The addition of rare earth to steel can change the composition, morphology, distribution and properties of inclusions in steel, thus improving various properties of steel, such as toughness, weldability and cold working performance. The wear resistance of ploughshare steel can be improved by adding rare earth.
