Stainless steel is the abbreviation of stainless and acid-resistant steel. The steel grades that are resistant to weak corrosive media such as air, steam, and water, or have stainless properties are called stainless steel; The steel type is called acid-resistant steel. Common products are
stainless steel seamless pipes and welded pipes.
The term "stainless steel" does not simply refer to one kind of stainless steel, but refers to more than one hundred kinds of industrial stainless steels, and each developed stainless steel has good performance in its specific application field. The key to success is first to understand the purpose, and then to determine the correct steel grade. There are usually only six steel grades relevant to building construction applications. They all contain 17-22% chromium, and the better steel grades also contain nickel. Adding molybdenum can further improve the atmospheric corrosion resistance, especially the resistance to chloride-containing atmosphere corrosion. Generally speaking, the hardness of stainless steel is higher than that of aluminum alloy, and the cost of stainless steel is higher than that of aluminum alloy.
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 organizational state. In addition, it can be divided into: chromium stainless steel, chromium-nickel stainless steel and chromium manganese nitrogen stainless steel. There is also a special stainless steel "GB24511_2009_Stainless steel plate and strip for pressure equipment" used for pressure vessels.
Ferritic stainless steel:
Chromium 15% to 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is better than other types of stainless steel, such as Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Ferritic stainless steel has good corrosion resistance and oxidation resistance because of its high chromium content, but its mechanical properties and process performance are poor. It is mostly used for acid-resistant structures with little stress and as anti-oxidation steel. This type of steel can resist the corrosion of the atmosphere, nitric acid and salt 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 used to make parts that work at high temperatures, such as gas turbine parts, etc. .
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 overall performance, resistant to corrosion by various media. Common 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, which makes the steel austenitic at room temperature. This type 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. Linings, pipelines, nitric acid-resistant equipment parts, etc., and can also be used as the main material of stainless steel watch accessories. Austenitic stainless steel generally adopts solution treatment, 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 steels:
It has the advantages of both austenitic and ferritic stainless steels, and has superplasticity. Austenite and ferrite each account for about half of the stainless steel. In the case of low carbon content, the content of chromium (Cr) is 18%~28%, and the content of nickel (Ni) is 3%~10%. Some steels also contain alloying elements such as Mo, Cu, Si, Nb, Ti, and N. This type of steel has the characteristics of both austenitic 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, and at the same time maintains iron The body stainless steel is brittle at 475°C, has high thermal conductivity, and has the characteristics of superplasticity. Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel.
Precipitation hardened stainless steel:
The matrix is austenite or martensite, and the commonly used grades of precipitation hardening stainless steel are 04Cr13Ni8Mo2Al and so on. It is a 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. The commonly used grades of martensitic stainless steel are 1Cr13, 3Cr13, etc., because of the high carbon content, it has high strength, hardness and wear resistance, but the corrosion resistance is slightly poor, and it is used for high mechanical properties and corrosion resistance. Some general parts are required, 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 plates and strips 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, signs and product quality certificates. The commonly used grades are 06Cr19Ni10, 022Cr17Ni12Mo2, and the digital codes are: S30408, S31603, etc. Mainly used in food machinery, pharmaceutical machinery and other sanitary equipment.
Tips: Grade 316 stainless steel tube is a high grade and shares many of the same characteristics as 304 stainless steel tube. One big difference is that it consists of 16 percent chromium content, 10 percent nickel content and two percent molybdenum.
Nickel and molybdenum increase its corrosion resistance against chlorides and reduce its susceptibility to pitting and cracking. Stainless steel also has additional corrosion resistance, which makes it a good choice for high-saline environments (i.e., coastal regions and areas where de-icing is used) and industrial applications involving chemical processes.
