stainless steel
In layman's terms, stainless iron is iron that is not easily rusted. In fact, some of the stainless steel has both rust and acid resistance (corrosion resistance). The rust and corrosion resistance of stainless iron is due to the formation of a chromium-rich oxide film (passivation film) on its surface. This rust and corrosion resistance are relative. The test shows that the corrosion resistance of iron in the weak medium such as atmosphere and water and the oxidizing medium such as nitric acid increases with the increase of the water content of chromium in the iron. When the chromium content reaches a certain percentage, the corrosion resistance of iron occurs. Mutations, from rust to rust, from corrosion to corrosion. There are many methods for classifying stainless iron. Classified according to the structure of the room temperature, there are martensite, austenite, ferrite and duplex stainless steel; according to the main chemical composition, can be basically divided into chromium stainless iron and chromium nickel stainless iron Large system; according to the use of nitric acid-resistant stainless steel, sulfuric acid-resistant stainless steel, seawater-resistant stainless steel, etc., according to the type of corrosion resistance can be divided into pitting corrosion-resistant stainless steel, stress corrosion-resistant stainless iron, Resistance to intergranular corrosion, stainless steel, etc.; classified according to functional characteristics can be divided into non-magnetic stainless iron, easy-cut stainless steel, low-temperature stainless iron, high-strength stainless iron and so on. Due to its excellent corrosion resistance, formability, compatibility and toughness over a wide temperature range, stainless steel is widely used in heavy industry, light industry, household goods industry and architectural decoration industries. Applications.
Austenitic stainless iron
Stainless iron having an austenite structure at normal temperature. When the iron contains about 18% of Cr, 8% to 10% of Ni, and about 0.1% of C, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the famous 18Cr-8Ni iron and a high Cr-Ni series iron which is developed by adding Cr, Ni content and adding elements such as Mo, Cu, Si, Nb and Ti. Austenitic stainless iron is non-magnetic and has high toughness and plasticity, but its strength is low, it is impossible to strengthen it by phase transformation, and it can only be strengthened by cold working. If S, Ca, Se, Te and other elements are added, it has good machinability. In addition to the corrosion resistance of the oxidizing acid medium, such iron can be resistant to corrosion by sulfuric acid, phosphoric acid, formic acid, acetic acid, urea, etc., if it contains elements such as Mo and Cu. If the carbon content of such iron is less than 0.03% or contains Ti or Ni, the intergranular corrosion resistance can be remarkably improved. High silicon austenitic stainless iron concentrated nitric acid has good corrosion resistance. Due to its comprehensive and good comprehensive properties, austenitic stainless steel has been widely used in various industries.
Ferritic stainless iron
Stainless iron mainly composed of ferrite in use. The chromium content is between 11% and 30%, and has a body-centered cubic crystal structure. This kind of iron generally does not contain nickel, and sometimes contains a small amount of Mo, Ti, Nb and other elements. Such iron has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance and excellent resistance to stress corrosion. Parts that are corroded by water vapor, water, and oxidizing acids. This type of iron has the disadvantages of poor plasticity, post-weld plasticity and corrosion resistance, which limits its application. The application of refining technology (AOD or VOD) can greatly reduce the interstitial elements such as carbon and nitrogen, thus making this type of iron widely used.
Austenite--ferrite duplex stainless steel
It is a stainless steel that accounts for about half of the austenite and ferrite structures. In the case of a lower C content, the Cr content is between 18% and 28%, and the Ni content is between 3% and 10%. Some irons also contain alloying elements such as Mo, Cu, Si, Nb, Ti, and N. This type of iron combines the characteristics of austenite and ferritic stainless iron. Compared with ferrite, it has higher plasticity, toughness, no room temperature brittleness, resistance to intergranular corrosion and weldability, and also maintains It has 475°C brittleness and high thermal conductivity of ferrite stainless iron, and it has superplasticity. Compared with austenitic stainless iron, it has high strength and resistance to intergranular corrosion and chloride stress corrosion resistance. Biphasic stainless steel has excellent pitting resistance and is also a nickel-free stainless steel.
Martensite stainless iron
The stainless steel whose mechanical properties can be adjusted by heat treatment is, in layman's terms, a kind of hardened stainless iron. Typical grades are Cr13, such as 2Cr13, 3Cr13, 4Cr13, etc. After fire, the hardness is higher. Different tempering temperatures have different combinations of toughness and are mainly used for steam turbine blades, tableware and surgical instruments. According to the difference in chemical composition, martensite stainless iron can be divided into martensite ferrochrome and martensitic chrome-nickel iron. According to different organization and strengthening mechanism, it can be divided into martensite stainless iron, martensite and semi-austenite (or semi-martensitic) precipitation hardening stainless iron and maraging rust iron.
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