Main types of stainless steel

Stainless steel is often divided into martensitic steel, ferritic steel, austenitic steel, austenitic ferritic (duplex) stainless steel and precipitation hardening stainless steel, etc. In addition, according to the composition can be divided into: chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel. There are also special stainless steel for pressure vessels "GB24511_2009_Stainless steel plate and steel strip for pressure equipment".
Ferrite stainless steel
Contains 15% ~ 30% chromium. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and the chloride stress corrosion resistance is better than other types of stainless steel, which belongs to this category Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and so on. Because of its high chromium content, ferritic stainless steel has good corrosion resistance and oxidation resistance, but its mechanical properties and process properties are poor, and it is mostly used for acid-resistant structures with little force and for antioxidant steel. This kind of steel can resist the corrosion of atmosphere, nitric acid and brine solution, and has the characteristics of high temperature oxidation resistance, low thermal expansion coefficient, etc., used in nitric acid and food factory equipment, and can also make parts that work at high temperatures, such as gas turbine parts.
Austenitic stainless steel
Chromium content is greater than 18%, but also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, can resist a variety of media corrosion. The common grades of austenitic stainless steel are 1Cr18Ni9, 0Cr19Ni9 and so on. The Wc of 0Cr19Ni9 steel is less than 0.08%, and the steel number is marked as "0". This kind of steel contains a large amount of Ni and Cr, so that the steel is austenitic at room temperature. This kind of steel has good plasticity, toughness, weldability, corrosion resistance and no magnetic or weak magnetism, corrosion resistance in oxidizing and reducing media are good, used to make acid-resistant equipment, such as corrosion resistant containers and equipment lining, transportation pipes, nitric acid resistant equipment parts, etc., in addition, it can also be used as the main material of stainless steel watch jewelry. Austenitic stainless steel generally uses solid solution treatment, that is, the steel is heated to 1050 ~ 1150 ° C, and then water-cooled or air-cooled to obtain single-phase austenitic structure.
Austenitic-ferrite duplex stainless steel
It has the advantages of austenitic and ferritic stainless steel and has superplasticity. Stainless steel with about half austenitic and half ferritic structure. In the case of low carbon content, the chromium (Cr) content is 18% to 28%, and the nickel (Ni) content is 3% to 10%. Some steels also contain Mo, Cu, Si, Nb, Ti, N and other alloying elements. This kind of steel has the characteristics of austenitic and ferritic stainless steel, compared with ferritic, higher plasticity, toughness, no room temperature brittleness, intergranular corrosion resistance and welding performance are significantly improved, while also maintaining the ferritic stainless steel 475℃ brittleness and high thermal conductivity, with superplasticity and other characteristics. Compared with austenitic stainless steel, it has higher strength and higher resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting resistance and is also a nickel-free stainless steel.