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About stainless steel

Published date : 2020/10/13 Views :

Stainless steel is the abbreviation of stainless steel acid resistance, resistance to air, steam, water and other weak corrosive medium or stainless steel is called stainless steel; And will be resistant to chemical corrosion medium (acid, alkali, salt and other chemical etching) corrosion of steel known as acid resistant steel.

Because of the difference in the chemical composition of the two and their corrosion resistance is different, ordinary stainless steel is generally not resistant to chemical medium corrosion, and acid resistant steel is generally rust resistance. The term "stainless steel" is not simply a kind of stainless steel, but means more than one hundred industrial stainless steel, each developed stainless steel has good performance in its specific application areas. The key to success is to know the purpose first, and then to determine the right type of steel. There are usually only six types of steel related to the application field of building construction. They contain between 17 and 22% chromium, and the better steels contain nickel. The addition of molybdenum can further improve atmospheric corrosion, especially the resistance to chlorinated atmospheric corrosion.


1. Main types


Stainless steel is often divided into: martensitic steel, ferrite steel, austenitic steel, austenitic - ferrite (duplex) stainless steel and precipitation hardening stainless steel, etc. Additional, can divide according to composition: chromium-stainless steel, chromium-nickel stainless steel and chromium-Manganese nitrogen stainless steel. There are also special stainless steel used for pressure vessels GB24511_2009_ stainless steel plates and belts for pressure equipment.


Ferritic stainless steel


Contains chromium 15% ~ 30%. The corrosion resistance, toughness and weldability are improved with the increase of chromium content, and the chloride stress corrosion resistance is better than other kinds of stainless steel, which includes Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Ferritic stainless steel because of the high content of chromium, corrosion resistance and oxidation resistance are better, but the mechanical performance and process performance is poor, more for less stress acidproof structure and oxidation resistance steel used. This kind of steel can resist the corrosion of atmosphere, nitric acid and saline solution, and has the characteristics of high temperature oxidation resistance, small thermal expansion coefficient, etc., used in nitric acid and food factory equipment, but also can be made in high temperature working parts, such as gas turbine parts.


Austenitic stainless steel


Contains more than 18% chromium, about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Comprehensive performance is good, can withstand a variety of medium corrosion. The commonly used grades of austenitic stainless steel are 1Cr18Ni9, 0Cr19Ni9, etc. 0Cr19Ni9 steel Wc<0.08%, marked as "0" in the steel number. This type of steel contains a large amount of Ni and Cr, which makes the steel in austenite state at room temperature. This kind of steel has good plasticity and toughness, weldability and corrosion resistance and non-magnetic or weak magnetic, the corrosion resistance in oxidizing and reducing medium are good, used to make acid equipment, such as corrosion resistant containers and equipment lining, pipelines, nitric acid resistant equipment parts, etc., also can be used as the main body of watches and clocks jewelry stainless steel material. Austenitic stainless steel generally adopts solid solution treatment, that is, the steel is heated to 1050 ~ 1150℃, and then water or air cooling, in order to obtain single-phase austenitic structure.


Austenitic - ferrite duplex stainless steel


It has the advantages of austenite and ferritic stainless steel, and has superplasticity. Stainless steel with austenite and ferrite structures each accounting for about half. When the content of C is low, the content of Cr and Ni ranges from 18% to 28% and 3% to 10% respectively. Some steels also contain alloying elements such as Mo, Cu, Si, Nb, Ti and N. This kind of steel has the characteristics of austenite and ferritic stainless steel. Compared with ferritic steel, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance. Meanwhile, it also has the characteristics of 475℃ brittleness, high thermal conductivity and superplasticity. Compared with austenitic stainless steel, its strength is higher and its resistance to intercrystalline corrosion and chloride stress corrosion is improved obviously. Duplex stainless steel has excellent corrosion resistance and is also a nickel - saving stainless steel.


Precipitation hardened stainless steel


The matrix is austenitic or martensite structure, precipitation hardened stainless steel commonly used grades are 04Cr13Ni8Mo2Al. Stainless steel that is hardened by precipitation hardening (also known as aging hardening) treatment.


Martensitic stainless steel


High strength, but poor plasticity and weldability. Martensite stainless steel commonly used brands are 1Cr13, 3Cr13, etc., because of high carbon content, it has a higher strength, hardness and wear resistance, but the corrosion resistance is slightly poor, used for mechanical performance requirements higher, corrosion resistance requirements of general some parts, such as spring, steam turbine blade, hydraulic press valve. This type of steel is used after quenching and tempering. Annealing is required after forging and stamping.


Stainless steel plates and belts for pressure equipment


Special stainless steel for pressure vessels, with specific requirements for classification and codes, dimensions, shapes and allowable deviations, technical requirements, test methods, inspection rules, packaging, marks and product quality certificates, etc. The commonly used brands are 06Cr19Ni10, 022Cr17Ni12Mo2, the numerical code is: S30408, S31603, etc. Mainly used for food machinery, pharmaceutical machinery and other health - grade equipment.


2. Main features




Stainless steel sculpture products for different USES of welding performance requirements are also different. A kind of tableware generally does not do the request to the welding performance, even includes part of the pot kind enterprise. But the vast majority of products need good welding performance of raw materials, like second-class tableware, thermos cup, steel pipe, water heater, water dispenser and so on.

Corrosion resistance


The vast majority of stainless steel products for corrosion resistant performance is good, like a, 2 kinds of tableware, kitchen utensils and appliances, water heaters, water dispensers, etc., some foreign businessmen on corrosion resistance of products also do experiment: in NACL aqueous solution heated to boiling, after a period of time the best solution, wash and drying, weight loss, to determine the degree of corrosion (note: the product polishing, because of the sand cloth or sandpaper containing Fe, will cause the test surface rust spots)


Polishing performance


Today's society stainless steel products in the production of general polishing this process, only a few products such as water heaters, water dispenser, such as tank do not need polishing. Therefore, this requires good polishing performance of raw materials. The main factors affecting the polishing performance are as follows:



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