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Main types of stainless steel
The term "stainless steel" does not simply refer to a stainless steel, but refers to more than one hundred industrial stainless steels, each of which has been developed with good performance in its specific application field. The key to success is to first understand the use, and then determine the correct steel. There are usually only six types of steel related to the application of building construction. They all contain 17 to 22% chromium, and the better steel also contains nickel. The addition of molybdenum may further improve atmospheric corrosion, particularly corrosion resistance to chloride-containing atmospheres.
Stainless steel is often divided into: martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic (duplex) stainless steel and precipitation hardening stainless steel. In addition, it can be divided into: chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel.
ferritic stainless steel
Chromium 12% ~ 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, chloride stress corrosion resistance is better than other types of stainless steel, belonging to this category of Crl7, Cr17Mo2Ti, Cr25,Cr25Mo3Ti, Cr28 and so on. Ferritic stainless steel because of the high chromium content, corrosion resistance and oxidation resistance are better, but the mechanical properties and process performance is poor, more for the force is not large acid resistant structure and for the use of oxidation resistance steel. This kind of steel can resist the corrosion of atmosphere, nitric acid and brine solution, and has the characteristics of good high temperature oxidation resistance and small thermal expansion coefficient. It is used in nitric acid and food factory equipment, and can also be made to work 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. Good comprehensive performance, resistance to a variety of media corrosion. The common grades of austenitic stainless steel are 1 Cr18Ni9, 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, welding, corrosion resistance and non magnetic or weak magnetic, in the oxidation and reduction of the medium corrosion resistance are good, used to make acid resistant equipment, such as corrosion resistant containers and equipment lining, pipeline, nitric acid resistant equipment parts, etc., can also be used as the main material of stainless steel watch jewelry. Austenitic stainless steel generally adopts solid solution treatment, that is, the steel is heated to 1050~1150 ℃, and then water-cooled or air-cooled to obtain a single-phase austenitic structure.
Austenitic-ferritic duplex stainless steel
It has the advantages of austenitic and ferritic stainless steel, and has superplasticity. Austenite and Ferrite Structure
Each accounts for about half of the stainless steel. In the case of low C content, Cr content in 18% ~ 28%,Ni content in 3% ~ 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 ferrite, plasticity, toughness is higher, no room temperature brittleness, intergranular corrosion resistance and welding performance are significantly improved, while maintaining the ferritic stainless steel 475 ℃ brittleness and high thermal conductivity, with superplasticity and other characteristics. Compared with austenitic stainless steel, high strength and resistance to intergranular corrosion and chloride stress corrosion resistance is significantly improved. Duplex stainless steel has excellent pitting corrosion resistance and is also a kind of nickel-saving stainless steel.
precipitation hardening stainless steel
The matrix is austenitic or martensitic structure, and the common grades of precipitation hardening stainless steel are 04Cr13Ni8Mo2Al, etc. Stainless steel that can be hardened (strengthened) by precipitation hardening (also known as age hardening).
martensitic stainless steel
High strength, but poor plasticity and weldability. Martensitic stainless steel commonly used grades are 1Cr13, 3Cr13, etc., because of the high carbon content, it has high strength, hardness and wear resistance, but the corrosion resistance is slightly worse, for high mechanical properties, corrosion resistance performance requirements of some of the general parts, such as springs, turbine blades, hydraulic press valves. This kind of steel is used after quenching and tempering. Annealing is required after forging and stamping.
Stainless steel is divided into austenitic stainless steel, ferritic stainless steel, duplex stainless steel, martensitic stainless steel and precipitation hardening stainless steel according to its organizational structure.
1. austenitic stainless steel
Austenitic stainless steel is an important class of stainless steel, and its output and dosage account for 70% of the total stainless steel. According to the alloying method, austenitic stainless steel can be divided into two categories: chromium-nickel steel and iron-chromium-manganese steel. The former uses nickel as the austenitizing element and is the main body of austenitic steel; the latter uses manganese and nitrogen instead of expensive nickel-saving steel.
Generally speaking, austenitic steel has good corrosion resistance, good comprehensive mechanical properties and process performance, but its strength and hardness are low.
2. ferritic stainless steel
Ferritic stainless steel containing chromium 11%-30%, basically does not contain nickel, is a nickel-saving steel, in the use of the state of the organization structure to ferrite-based.
Ferritic stainless steel has high strength, low cold work hardening tendency, excellent resistance to chloride stress corrosion, pitting corrosion, crevice corrosion and other local corrosion performance, but sensitive to intergranular corrosion, low temperature toughness is poor.
3. duplex stainless steel
It is generally believed that there is more than 15% ferrite on the austenite matrix, or more than 15% austenite on the ferrite matrix can be called austenite + ferrite duplex stainless steel.
Duplex stainless steel has the advantages of both austenitic steel and ferritic steel.
4. marhalanobis type stainless steel
Martensitic stainless steel is a kind of steel whose performance can be adjusted by heat treatment, and its strength and hardness are high.
5. precipitation hardening stainless steel
Precipitation hardening stainless steel is a steel that precipitates carbides in the steel by means of heat treatment, so as to improve the strength of the steel.
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