铬合金作用（Chromium alloy action）1, carbon (C): the increase of carbon content in steel, yield point and tensile strength increased, but the plasticity and impact resistance decreased, when the carbon content of more than 0.23%, bad welding properties of the steel, so for low alloy structural steel welding, the carbon content is generally not more than 0.20%. High carbon content will also reduce the atmospheric corrosion resistance of steel. It is easy to rust in high carbon steel in open air field; in addition, carbon can increase cold brittleness and aging sensitivity of steel.2, silicon (Si): in the process of steelmaking with silicon as a reducing agent and deoxidizer, so calm steel contains 0.15 - 0.30% of silicon. If there is more than 0.50-0.60% silicon in the steel, silicon is alloying. Silicon can significantly increase the elastic limit, yield point and tensile strength of steel, so it is widely used as spring steel. Join the 1.01.2% silicon in the quenched and tempered steel, strength can be increased by 15-20%. The combination of silicon, molybdenum, tungsten and chromium can improve the corrosion resistance and oxidation resistance, and can be used to manufacture heat-resistant steel. Low carbon steel containing silicon 1 - 4%, with a high permeability, used in electrical industry silicon steel sheet. The increase in silicon will reduce the weldability of steel.3, manganese (Mn): in the process of steelmaking, manganese is a good deoxidizer and desulfurizer, manganese in general steel 0.30 - 0.50%. In carbon steel, adding more than 0.70% even when the steel, compared with the general volume of steel steel not only has enough toughness, and high strength and hardness, improve the hardenability of steel, improve the thermalperformance of steel, such as 16Mn A3 40% high yield point steel ratio. Steel containing Mn 11 - 14% has very high abrasion resistance. It is used in excavator bucket, ball mill lining board and so on. The manganese content increases, weakens the steel corrosion resistance, reduces the welding performance.4, phosphorus (P): in general, phosphorus is a harmful element in steel, increasing cold brittleness of steel, making welding performance worse, reducing plasticity, and making cold bending property deteriorate. Therefore, steel is usually required to contain less than 0.045% phosphorus, high quality steel requirements are lower.5, sulfur (S): sulfur is, in general, also a harmful element. To cause hot brittleness of steel, to reduce the ductility and toughness of steel, and to cause cracks in forging and rolling. Sulfur is also detrimental to weldability and reduces corrosion resistance. Therefore, sulfur content is usually less than 0.055%, high quality steel requirements are less than 0.040%. The addition of 0.08-0.20% sulfur in steel improves machinability, often referred to as free cutting steel.6 chromium (Cr): in structural steel and tool steel, chromium can significantly increase strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium can also improve the oxidation resistance and corrosion resistance of steel, which is an important alloying element of stainless steel and heat-resistant steel.7, nickel (Ni): nickel can improve the strength of steel, while maintaining good plasticity and toughness. Nickel has higher corrosion resistance to acid and base, and has the ability of rust prevention and heat resistance under high temperature. But because the nickel is a scarce resource, it should try to use other alloying elements substitution of nickel chromium steel.8, molybdenum (Mo): molybdenum can make steel grain refinement, improve hardenability and thermal strength, at high temperature to maintain enough strength and creep resistance (long-term under high temperature stress, deformation, called creep). The addition of molybdenum into structural steel improves mechanical properties. It can also restrain the brittleness of alloy steel due to fire. Improve red in tool steel.9, titanium (Ti): titanium is a strong deoxidizer in steel. It can make the inner structure of steel compact, refine grain power, reduce aging sensitivity and cold brittleness. Improve welding performance. Adding proper titanium into chromium 18 nickel 9 austenitic stainless steel can avoid intergranular corrosion.10, vanadium (V): vanadium is a good deoxidizer of steel. 0.5% of the vanadium in the steel can refine the grain and improve the strength and toughness. The carbides formed by vanadium and carbon can improve hydrogen corrosion resistance under high temperature and high pressure.11, tungsten (W): Tungsten melting point is higher than the major, is the precious alloy element. Tungsten and carbon form tungsten carbide with high hardness and wear resistance. Adding tungsten in tool steel can significantly improve red hardness and thermal strength, and be used as cutting tools and forging dies.12 niobium (Nb):