Popularly speaking, stainless steel is not easy to rust steel, in fact, a part of stainless steel has both rust resistance and acid resistance (corrosion resistance). Stainless steel's rust resistance and corrosion resistance are due to the formation of chromium rich oxide film (passive film) on its surface. This kind of rust and corrosion resistance is relative. The test shows that the corrosion resistance of steel increases with the increase of chromium water content in the medium of atmosphere, water and other weak medium and nitric acid. When the chromium content reaches a certain percentage, the corrosion resistance of steel is abrupt, that is, from easy to rust to rust, and never corrosion resistance to corrosion resistance. There are many methods of classification for stainless steel. According to the structure of the room at room temperature, there are Martensitic, austenite, ferrite and duplex stainless steel. According to the main chemical composition, it can be divided into two major systems: chromium stainless steel and chrome nickel stainless steel. In accordance with the use, there are nitric acid stainless steel, sulphuric acid stainless steel, seawater resistant stainless steel and so on, according to corrosion resistance type. It can be divided into corrosion resistant stainless steel, stress corrosion resistant stainless steel, intergranular corrosion resistant stainless steel and so on. According to the functional characteristics, it can be divided into non magnetic stainless steel, easy cutting stainless steel, low temperature stainless steel, high strength stainless steel and so on. Because of its excellent corrosion resistance, formability, compatibility and strong and toughness in a wide range of temperature, stainless steel has been widely used in heavy industry, light industry, household goods industry and architectural decoration.
austenitic stainless steel
A stainless steel having austenitic microstructure at normal temperature. The steel contains about Cr of about 18%, Ni 8%~10% and C about 0.1%, and has a stable austenite structure. Austenitic chromium nickel stainless steel includes the famous 18Cr-8Ni steel and the high Cr-Ni series steel which is developed on this basis by adding Cr, Ni content and adding Mo, Cu, Si, Nb, Ti and other elements. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low. It can not be strengthened by phase transformation, and can only be strengthened by cold working. If S, Ca, Se, Te and other elements are added, it has good machinability. In addition to oxidizing acid medium corrosion, such steels contain Mo, Cu and other elements, which can also resist corrosion of sulfuric acid, phosphoric acid, formic acid, acetic acid and urea. If the carbon content in such steels is below 0.03% or Ti or Ni, the intergranular corrosion resistance can be significantly improved. High silicon austenitic stainless steel and concentrated nitric acid will have good corrosion resistance. Because austenitic stainless steel has comprehensive and good comprehensive properties, it has been widely applied in all walks of life.
Ferritic stainless steel
Stainless steel is mainly used as ferrite in the service state. The chromium content is 11%~30% and has a bcc structure. This kind of steel generally does not contain nickel, and sometimes contains a small amount of Mo, Ti, Nb and other elements. This kind of steel has the characteristics of high thermal conductivity, small expansion coefficient, good oxidation resistance, good resistance to stress corrosion and so on. It is used for the manufacture of parts which are resistant to atmospheric, water vapor, water and oxidizing acid corrosion. This kind of steel has disadvantages such as poor plasticity, reduced plasticity and corrosion resistance after welding, which limits its application. The application of external refining technology (AOD or VOD) can greatly reduce the gap elements such as carbon and nitrogen.
Austenite ferritic duplex stainless steel
It is about half the stainless steel of austenite and ferrite. In the case of low C content, Cr content is 18%~28% and Ni content is 3%~10%. Some steels also contain Mo, Cu, Si, Nb, Ti, N and other alloy elements. This kind of steel has the characteristics of austenite and ferritic stainless steel. Compared with ferrite, it has higher plasticity, toughness, no room temperature brittleness, intergranular corrosion resistance and welding performance. At the same time, the brittleness of ferritic stainless steel at 475 C, high thermal conductivity and superplasticity are also maintained. Compared with austenitic stainless steel, the strength is high, and intergranular corrosion and chloride stress corrosion resistance are significantly improved. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel saving stainless steel.
Martensitic stainless steel
Stainless steel, which can adjust its mechanical properties through heat treatment, is a kind of hardened stainless steel, popularly speaking. Typical brands are Cr13, such as 2Cr13, 3Cr13, 4Cr13, etc. Hardened after the fire