Stainless steel is often classified according to the state of organization: martensitic steel, ferrite steel, austenitic steel, austenitic - ferrite (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 according to its composition.
1. Ferrite stainless steel
Generally containing 15% to 30% chromium. Its corrosion resistance, toughness and weldability with the increase in chromium content, chloride stress corrosion resistance is better than other types of stainless steel, belonging to this category are Crl7. Cr17Mo2Ti, Cr25. Cr25Mo3Ti, Cr28 and so on. Ferritic stainless steel because of the high chromium content, corrosion resistance and oxidation resistance are relatively good, but the mechanical properties and process performance is poor, mostly used for the force is not big acid-resistant structure and oxidation-resistant steel use. This kind of steel can resist the corrosion of the atmosphere, nitric acid and brine solution, and has good high temperature oxidation resistance, small coefficient of thermal expansion, etc., used in nitric acid and food factory equipment, can also make the parts working at high temperature, such as gas turbine parts.
2. Austenitic stainless steel
Generally contains more than 18% chromium, also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Comprehensive performance is good, can be resistant to a variety of media corrosion. Austenitic stainless steel commonly used grades are 1Cr18Ni9. 0Cr19Ni9 and so on. This type of steel contains a large amount of nickel and chromium, so that the steel is austenitic at room temperature. This type of steel has good plasticity, toughness, weldability, corrosion resistance and non-magnetic or weakly magnetic, corrosion resistance in oxidizing and reducing media are better, used to make acid-resistant equipment, such as corrosion-resistant containers and equipment lining, conveying pipelines, nitric acid-resistant equipment parts, etc., and also used as a stainless steel watch jewelry body material. Austenitic stainless steel is generally solid solution treatment, that is, the steel is heated to 1050 ~ 1150 ℃, and then water-cooled or air-cooled, in order to obtain a single-phase austenitic organization.
3. Austenitic - ferritic duplex stainless steel
Both austenitic and ferritic stainless steel advantages, and has superplasticity. Austenitic and ferritic organizations each account for about half of the stainless steel. In the case of low carbon content, chromium content of 18% to 28%, nickel content of 3% to 10%. Some steels also contain Mo, Cu, Si, Nb, Ti, N and other alloying elements. This type of steel has both austenitic and ferritic stainless steel, compared with ferritic, plasticity, toughness is higher, no room temperature brittleness, intergranular corrosion resistance and welding performance are significantly improved, while also maintaining a ferritic stainless steel brittleness 475 ℃, as well as high thermal conductivity, superplasticity and other characteristics. Compared with austenitic stainless steel, high strength and resistance to intergranular corrosion and chloride stress corrosion has improved significantly. Duplex stainless steel has excellent resistance to pore corrosion, is also a nickel-saving stainless steel.
4. precipitation hardening stainless steel
The matrix is austenitic or martensitic organization, precipitation hardening stainless steel commonly used grades such as 04Cr13Ni8Mo2Al. It can be precipitation hardening (also known as age hardening) treatment to make it hardened stainless steel.
5. 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, so it has high strength, hardness and abrasion resistance, but the corrosion resistance is slightly worse, used for mechanical properties require high, corrosion resistance requirements of general some parts, such as springs, turbine blades, hydraulic valves, and so on. These steels are used after quenching and tempering treatment, and need to be annealed after forging and stamping.
