Stainless steel is often divided into martensitic steel, ferritic steel, austenitic steel and so on. In addition, it can be divided into chromium stainless steel, chrome nickel stainless steel, chromium manganese nitrogen stainless steel and so on.
Ferritic stainless steel: chromium containing 12% ~ 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and chloride resistance is better than other kinds of stainless steel.
Belonging to this category are Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and so on. Ferritic stainless steel has good corrosion resistance and antioxidant properties because of its high chromium content, but poor mechanical and technological properties. It is used in acid resistant structure and used as antioxidant steel. 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 low coefficient of thermal expansion. It is used in nitric acid and food factory equipment, and can also make parts working at high temperature, such as gas turbine parts and so on.
Austenitic stainless steel: chromium is more than 18%, also contains about 8% of nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and can endure a variety of medium corrosion.
The commonly used grades of austenitic stainless steel are 1Cr18Ni9 and 0Cr19Ni9. 0Cr19Ni9 steel wC < 0.08%, steel number marked "0". This kind of steel contains a lot of Ni and Cr, which makes the steel austenite at room temperature. This kind of steel has good plasticity, toughness, weldability and corrosion resistance. It has good corrosion resistance in oxidizing and reductive medium. It is used to make acid resistant equipment, such as corrosion resistant container and equipment lining, pipeline, and nitric acid resistant equipment parts. Austenitic stainless steel is usually treated by solid solution. The steel will be heated to 1050~1150 degrees and then cooled to obtain single phase austenite.
Austenitic ferrite duplex stainless steel has the advantages of both austenitic and ferritic stainless steels, and has superplasticity.
Austenite and ferrite constitute about half of the stainless steel. In the case of low C content, Cr content is 18%~28% and Ni content is 3%~10%. Some steels also contain Mo, Cu, Si, Nb, Ti, N and other alloy elements. This kind of steel has the characteristics of austenite and ferritic stainless steel. Compared with ferrite, it has higher plasticity, toughness, no room temperature brittleness, intergranular corrosion resistance and welding performance. At the same time, the brittleness of ferritic stainless steel at 475 C, high thermal conductivity and superplasticity are also maintained. Compared with austenitic stainless steel, the strength is high, and intergranular corrosion and chloride stress corrosion resistance are significantly improved. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel saving stainless steel.
Martensitic stainless steel: high strength, but poor plasticity and weldability.
The common brand of martensitic stainless steel is 1Cr13, 3Cr13 and so on. Because of its high carbon content, it has high strength, hardness and wear resistance, but the corrosion resistance is poor. Some parts, such as spring, turbine blade, hydraulic press valve, are used for high mechanical properties and corrosion resistance. This kind of steel is used after quenching and tempering.