The 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 according to the microstructure. In addition, it can be divided into chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel according to the composition. There is also a special stainless steel for pressure vessels "Stainless steel plates and steel strips for GB24511_2009_ pressure equipment".

Ferritic stainless steel
Chromium content 15%~30%. Its corrosion resistance, toughness and weldability are improved with the increase of chromium content, and the chloride stress corrosion resistance is better than that of other types of stainless steel, which belong to this category of Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Because of its high chromium content, ferritic stainless steel has good corrosion resistance and oxidation resistance, but poor mechanical and technological properties, and is mostly used in acid-resistant structures with little stress and oxidation-resistant steel. This kind of steel can resist the corrosion of atmosphere, nitric acid and brine solution, and has the characteristics of good oxidation resistance at high temperature and small thermal expansion coefficient, which is used for nitric acid and food factory equipment, and can also be used to make parts that work at high temperatures, such as gas turbine parts.

Austenitic stainless steel
The chromium content is greater than 18%, and it also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and can resist corrosion of a variety of media. The commonly used grades of austenitic stainless steel are 1Cr18Ni9, 0Cr19Ni9 and so on. The Wc of 0Cr19Ni9 steel is less than 0.08% and is marked with "0" in the steel grade. This type of steel contains a large amount of Ni and Cr, which gives the steel an austenite state at room temperature. This kind of steel has good plasticity, toughness, weldability, corrosion resistance and non-magnetic or weak magnetism, and has good corrosion resistance in oxidizing and reducing media, and is used to make acid-resistant equipment, such as corrosion-resistant containers and equipment linings, transportation pipelines, nitric acid-resistant equipment parts, etc., and can also be used as the main material of stainless steel watch jewelry. Austenitic stainless steel is generally treated with solid solution, that is, the steel is heated to 1050~1150 °C, and then water-cooled or air-cooled to obtain a single-phase austenite structure.

Austenitic-ferritic duplex stainless steel
It combines the advantages of austenitic and ferritic stainless steels with superplasticity. Stainless steel, which has an austenitic and ferritic structure, accounts for about half each. In the case of low carbon content, the chromium (Cr) content is 18%~28%, and the nickel (Ni) content is 3%~10%. Some steels also contain alloying elements such as Mo, Cu, Si, Nb, Ti, N, etc. Compared with ferrite, this kind of steel has the characteristics of austenitic and ferritic stainless steel, higher plasticity, toughness, no brittleness at room temperature, significant improvement in intergranular corrosion resistance and welding performance, and also maintains the brittleness of 475 °C and high thermal conductivity of ferritic stainless steel, with superplasticity and other characteristics. Compared with austenitic stainless steels, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent resistance to potting and corrosion, and it is also a nickel-saving stainless steel.

Precipitation hardening stainless steel
The matrix is austenitic or martensitic structure, and the commonly used grades of precipitation hardened stainless steel are 04Cr13Ni8Mo2Al, etc. It can be hardened (strengthened) by precipitation hardening (also known as age hardening).

Martensitic stainless steel
High strength, but poor plasticity and weldability. The commonly used grades of martensitic stainless steel are 1Cr13, 3Cr13, etc., because of the high carbon content, so it has high strength, hardness and wear resistance, but the corrosion resistance is slightly poor, and it is used for some parts with high mechanical property requirements and general corrosion resistance requirements, such as springs, steam turbine blades, hydraulic pressure valves, etc. This type of steel is used after quenching and tempering treatment. Annealing is required after forging and stamping.

Stainless steel plate and steel strip for pressure equipment
Stainless steel for pressure vessels has clear requirements for its classification and code, size, shape and allowable deviation, technical requirements, test methods, inspection rules, packaging, marking and product quality certificates. Commonly used grades are 06Cr19Ni10, 022Cr17Ni12Mo2, and the digital codes are: S30408, S31603, etc. It is mainly used for food machinery, pharmaceutical machinery and other sanitary equipment.