Stainless steel is often classified according to the state of organization: martensitic steel, ferritic steel, austenitic steel, etc.. In addition, it can be divided into: chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel, etc. according to the composition.
1, ferritic stainless steel: containing 12% 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, and is used for not much force acid-resistant structure and for the use of oxidation-resistant steel. This type of steel can resist the atmosphere, nitric acid and brine solution corrosion, and has a good high temperature oxidation resistance, small coefficient of thermal expansion, etc., used in nitric acid and food factory equipment, can also make parts working at high temperature, such as gas turbine parts. 2, austenitic stainless steel: 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, etc. 0Cr19Ni9 steel wC <0.08%, the steel number marked as "0". This type of steel contains a large amount of Ni and Cr, so that the steel at room temperature austenitic state. This type of steel has good plasticity, toughness, weldability and corrosion resistance, corrosion resistance in oxidizing and reducing media are better, used to make acid-resistant equipment, such as corrosion-resistant containers and equipment lining, piping, nitric acid-resistant equipment parts. Austenitic stainless steel is generally solution treated, that is, the steel is heated to 1050 ~ 1150 ℃, and then water-cooled to obtain a single-phase austenitic organization. 3, austenitic - ferrite duplex stainless steel: both austenitic and ferrite stainless steel, and has the advantages of superplasticity. Austenitic and ferritic organizations each account for about half of the stainless steel. In the case of low C content, Cr content of 18% ~ 28%, Ni content of 3% ~ 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 features, 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 475 ℃ brittleness and thermal conductivity is high, with 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 pore corrosion resistance, is also a nickel-saving stainless steel. 4, 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, it has high strength, hardness and wear resistance, but slightly poorer corrosion resistance, used for mechanical properties require high, corrosion resistance requirements of the general requirements of a number of parts, such as springs, turbine blades, hydraulic valves and so on. This type of steel is used after quenching and tempering treatment.