Stainless Steel Steel) is the abbreviation of stainless and acid-resistant steel, which is resistant to weak corrosive media such as air, steam, and water or is called stainless steel. The type of steel is called acid-resistant steel.

Due to the difference in chemical composition of the two, their corrosion resistance is different. Ordinary stainless steel is generally not resistant to chemical medium corrosion, while acid-resistant steel is generally stainless. The term "stainless steel" does not simply refer to one type of stainless steel, but to more than one hundred industrial stainless steels, each developed to perform well in its specific field of application. The key to success is to first understand the application and then determine the correct steel grade. There are usually only six steel grades associated with building construction applications. They all contain 17-22% chromium, and the better grades also contain nickel. The addition of molybdenum can further improve atmospheric corrosion, especially corrosion resistance to chloride-containing atmospheres.

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.

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 structure state. 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 are also special stainless steels for pressure vessels "GB24511_2009_ Stainless Steel Plates and Strips for Pressure Equipment".

Ferritic Stainless Steel

Contains 15% to 30% chromium. 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. Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Because of the high chromium content, ferritic stainless steel has good corrosion resistance and oxidation resistance, but poor mechanical properties and process performance. This kind of steel can resist the corrosion of the atmosphere, nitric acid and brine solution, and has the characteristics of good high temperature oxidation resistance and small thermal expansion coefficient. .

Austenitic stainless steel

Contains more than 18% chromium and also contains About 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and is resistant to corrosion by various media. The commonly used grades of austenitic stainless steel are 1Cr18Ni9, 0Cr19Ni9, etc. The Wc of 0Cr19Ni9 steel is less than 0.08%, which is marked as "0" in the steel number. This type of steel contains a large amount of Ni and Cr, which makes the steel in an austenitic state 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, conveying pipes, nitric acid-resistant equipment parts, etc., can also be used as the main material of stainless steel watch accessories. Austenitic stainless steel is generally solution-treated, that is, heating the steel to 1050-1150 °C, and then water-cooling or air-cooling to obtain a single-phase austenite structure.

Austenitic-ferritic duplex stainless steel

It has the advantages of both austenitic and ferritic stainless steels, and has superplasticity. 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 alloying elements such as Mo, Cu, Si, Nb, Ti, and N. This type of steel has the characteristics of both austenitic and ferritic stainless steels. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance. The 475 ℃ brittleness and high thermal conductivity of element stainless steel have 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.