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Austenitic stainless steel: stainless steel having an austenitic structure at normal temperature. When the steel contains about 18% Cr, 8%-10% Ni, and about 0.1% C, it has a stable austenite structure. Austenitic chrome-nickel stainless steel includes the famous 18Cr-8Ni steel and high-Cr-Ni series steel which is developed by adding Cr, Ni content and adding elements such as Mo, Cu, Si, Nb and Ti. Austenitic stainless steel 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 oxidizing acid medium, such steel can also resist the corrosion of 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 steel is less than 0.03% or contains Ti or Ni, the intergranular corrosion resistance can be remarkably improved. High silicon austenitic stainless steel has good corrosion resistance to nitric acid. Due to the comprehensive and good comprehensive properties of austenitic stainless steel, it has been widely used in various industries.
Ferritic stainless steel: stainless steel mainly composed of ferrite in use. The chromium content is between 11% and 30%, and has a body-centered cubic crystal structure. These steels generally do not contain nickel, and sometimes contain a small amount of elements such as Mo, Ti, Nb, etc. These steels are characterized by 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. Such steels have the disadvantages of poor plasticity, post-weld plasticity and corrosion resistance, which limit their application. The application of refining technology (AOD or VOD) can greatly reduce the gap elements such as carbon and nitrogen, thus making this type of steel widely used.
Austenitic-ferritic duplex stainless steel: stainless steel with approximately 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 steels also contain alloying elements such as Mo, Cu, Si, Nb, Ti, and N. This type of steel combines the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity, toughness, no room temperature brittleness, resistance to intergranular corrosion and weldability, and iron retention. The stainless steel has a brittleness at 475 ° C and a high thermal conductivity, and is characterized by superplasticity. Compared with austenitic stainless steel, it has high strength and resistance to intergranular corrosion and chloride stress corrosion resistance. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel.
Martensitic stainless steel: Stainless steel whose mechanical properties can be adjusted by heat treatment. Generally speaking, it is a kind of hardenable stainless steel. Typical grades are Cr13, such as 20Cr13, 30Cr13, 40Cr13, etc. After quenching, 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, martensitic stainless steel can be divided into martensite chromium steel and martensitic chromium nickel steel. According to the organization and strengthening mechanism, it can be divided into martensitic stainless steel, martensite and semi-austenitic (or semi-martensitic) precipitation hardening stainless steel and maraging stainless steel.
Representative steel grade, chemical composition, room temperature mechanical properties: the representative steel grade of martensitic stainless steel is 12Cr13, 20Cr13, 30Cr13, etc., the representative steel grade of ferritic stainless steel is 10Cr17, 10Cr17Mo, etc., the representative steel grade of austenitic stainless steel is 06Cr19Ni10 (304), 022Cr19Ni10 (304L), 06Cr17Ni12Mo2 (316), 022Cr17Ni12Mo2 (316L), 06Cr18Ni11Ti (321), 06Cr18Ni11Nb (347), etc., the representative steel of duplex stainless steel is 00Cr26Ni7Mo2Ti and so on.
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