Stainless steel is often divided into martensitic steels, ferritic steels, austenitic steels, austenitic-ferritic (duplex) stainless steels and precipitation-hardened stainless steels according to the structure state. In addition, it can be divided into: chrome stainless steel, chrome nickel stainless steel and chrome manganese nitrogen stainless steel.
Ferritic stainless steel
Contains 15% to 30% of chromium. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and the resistance to chloride stress corrosion resistance is better than other types of stainless steel. Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. belong to this category. Ferritic stainless steel has high corrosion resistance and oxidation resistance because of its high chromium content. However, its mechanical properties and process properties are poor. It is mostly used for acid-resistant structures with little stress and as oxidation-resistant steel. This type of steel can resist the corrosion of the atmosphere, nitric acid and saline solution, and has the characteristics of good high temperature oxidation resistance and low thermal expansion coefficient. It is used in nitric acid and food factory equipment, and it can also be made at high temperature, such as gas turbine parts.
Austenitic stainless steel
It contains more than 18% chromium, and also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Comprehensive performance, can withstand a variety of media corrosion. 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 the steel number is marked as "0". This type of steel contains a large amount of Ni and Cr, making the steel austenitic at room temperature. This kind of steel has good plasticity, toughness, weldability, corrosion resistance and non-magnetic or weak magnetic properties. It has good corrosion resistance in oxidizing and reducing media. It is used to make acid-resistant equipment, such as corrosion-resistant containers and equipment. Lining, pipelines, nitric acid-resistant equipment parts, etc. In addition, it can also be used as the main material of stainless steel watch accessories. The austenitic stainless steel is generally subjected to a solution treatment, that is, the steel is heated to 1050 to 1150 ° C, and then water-cooled or air-cooled to obtain a single-phase austenitic structure.
Austenitic-ferritic duplex stainless steel
It has the advantages of both austenitic and ferritic stainless steels, and has superplasticity. The austenitic and ferritic structures each account for about half of stainless steel. 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 alloy elements such as Mo, Cu, Si, Nb, Ti, and N. This type of steel has the characteristics of both austenite and ferritic stainless steel. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, significantly improved intergranular corrosion resistance and welding performance, while maintaining iron Element stainless steel has 475 ° C brittleness, high thermal conductivity, and superplasticity. Compared with austenitic stainless steel, it has higher strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting resistance and is also a nickel-saving stainless steel.
Precipitation hardened stainless steel
The matrix is austenite or martensite. Commonly used grades of precipitation hardened stainless steel are 04Cr13Ni8Mo2Al and so on. It can be hardened (strengthened) stainless steel by precipitation hardening (also known as aging 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 higher carbon content, it has higher strength, hardness and wear resistance, but the corrosion resistance is slightly worse. It is used for higher mechanical properties and corrosion resistance Requires some general parts, such as springs, steam turbine blades, hydraulic press valves, etc. This type of steel is used after quenching and tempering. Annealing is required after forging and stamping.
Stainless steel plate and strip for pressure equipment
There are clear requirements for the classification and code, size, shape and allowable deviation, technical requirements, test methods, inspection rules, packaging, marking and product quality certificate of stainless steel for pressure vessels. The commonly used grades are 06Cr19Ni10, 022Cr17Ni12Mo2, and the numerical codes are: S30408, S31603, and so on. Mainly used in food machinery, pharmaceutical machinery and other sanitary equipment.