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Stainless steel features Jun 12, 2018

Corrosion resistance of stainless steel decreases with the increase of carbon content. Therefore, most stainless steels have low carbon content, the maximum is not more than 1.2%, and some steels have Wc (carbon content) even lower than 0.03% (such as 00Cr12 ). The main alloying element in stainless steel is Cr (chromium). Only when the Cr content reaches a certain value, the steel has corrosion resistance. Therefore, stainless steel generally has a Cr (chromium) content of at least 10.5%. Stainless steel also contains elements such as Ni, Ti, Mn, N, Nb, Mo, Si, and Cu.

      Stainless steel is usually divided into martensitic steels, ferritic steels, austenitic steels, austenitic-ferritic (duplex) stainless steels, and precipitation hardened stainless steels. In addition, it can be divided into: chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel. The

1, ferritic stainless steel: chromium containing 12% to 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is superior to other types of stainless steel. Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and the like belong to this class. Ferritic stainless steel has high 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 less stress and for oxidation resistant steels. This kind of steel can resist the corrosion of atmosphere, nitric acid and saline solution, and has the characteristics of high temperature oxidation resistance and small thermal expansion coefficient. It can be used in nitric acid and food factory equipment, also can make parts working under high temperature, such as gas turbine parts, etc. .

2. Austenitic stainless steel: Chromium is more than 18%, also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, resistant to many media corrosion. The commonly used grades of austenitic stainless steels include 1Cr18Ni9 and 0Cr19Ni9. Wc < 0.08% for 0Cr19Ni9 steel and "0" for steel. This type of steel contains a large amount of Ni and Cr, making the steel austenitic at room temperature. This type of steel has good plasticity, toughness, weldability, corrosion resistance, and non-magnetic properties. It has good corrosion resistance in both oxidizing and reducing media. It is used to make acid-resistant equipment, such as corrosion-resistant containers and equipment linings, and transportation. Pipes, nitric acid-resistant equipment parts, etc., can also be used as the main material of stainless steel watch accessories. Austenitic stainless steels generally use solid solution treatment, that is, the steel is heated to 1050 ~ 1150 °C, and then water-cooled or air-cooled to obtain single-phase austenite.

3, austenitic - ferritic duplex stainless steel: both the advantages of austenitic and ferritic stainless steel, and has superplasticity. Austenite and ferrite are about half of stainless steel. In the case of lower C content, the Cr content is 18% to 28%, and the 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 combines the characteristics of austenitic and ferritic stainless steels. Compared with ferrite, it has higher plasticity and toughness, no brittleness at room temperature, significantly improved resistance to intergranular corrosion and welding performance, and at the same time retains iron. The 475°C brittleness and high thermal conductivity of the ferritic stainless steel make it superplastic. Compared with austenitic stainless steels, they have high strength and resistance to intergranular corrosion and chloride stress corrosion resistance. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-stainless steel.

4, martensitic stainless steel: high strength, but poor plasticity and weldability. The commonly used grades of martensitic stainless steels are 1Cr13, 3Cr13, etc. Because of the high carbon content, they have higher strength, hardness and wear resistance, but they are slightly inferior in corrosion resistance. They are used for high mechanical properties and corrosion resistance. General requirements for some parts, such as springs, turbine blades, hydraulic press valves. This kind of steel is used after quenching and tempering.

5. Precipitation hardening stainless steel: The matrix is austenite or martensite, and the commonly used grades of precipitation hardening stainless steel are 04Cr13Ni8Mo2Al. It can be treated by precipitation hardening (also known as age hardening) to make it hard (strong) stainless steel.