Ferritic stainless steel (400 series) contains 15% to 30% chromium and has a body-centered cubic crystal structure. These steels generally do not contain nickel, and sometimes contain a small number of elements such as Mo, Ti, Nb, etc. These steels have the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent resistance to stress corrosion, etc. Parts that are corroded by water vapor, water, and oxidizing acids. The price of ferritic stainless steel is not only relatively low and stable but also has many unique features and advantages. It has been proven that ferritic stainless steel is extremely rare in many applications where austenitic stainless steel (300 series) was originally considered to be used. Excellent alternative material, ferritic stainless steel does not contain nickel, the main elements are chromium (>10%) and iron, chromium is a particularly corrosion-resistant element of stainless steel, and its price is relatively stable.

Ferritic stainless steel can be generally divided into two types: ordinary ferritic stainless steel and high-purity ferritic stainless steel.

Ordinary ferritic stainless steel

Superferrite Tube, TP405, TP444, TP446

Such steels include low, medium, and high chromium content. Low-chromium ferritic stainless steel, containing about 11% to 14% chromium, such as 00Cr12, and 0Cr13Al in China. American AISI 400, 405, 406MF-2 (see table). Such steels have good toughness, plasticity, cold deformability, and weldability. Since steel contains a certain amount of chromium and aluminum, it has good oxidation resistance and rust resistance. 405 can be used as a petroleum refining tower, tank lining, steam turbine blades, high-temperature sulfur corrosion-resistant equipment, and the like. 400 is used as a home and office appliance. 409 is used in automobile exhaust noise reduction system devices and cold and warm water pipes. Medium-chromium ferritic stainless steel with a chromium content of 14% to 19%, such as Chinas 1Cr17 and 1Cr17Mo. AISI 429, 430, 433, 434, 435, 436, 439 of the United States. This type of steel has good rust resistance and corrosion resistance. Its work hardening coefficient is small (n≈2), and it has good deep drawing performance, but its ductility is poor. 430 is used as a component of architectural decoration, car decoration, kitchen equipment, gas burners, and nitric acid industrial equipment. 434 is used for the exterior decoration of cars and buildings. 439 is used as a hose for gas water heaters, coal, and gas pipelines. High-chromium ferritic stainless steel contains 19% to 30% chromium, such as Cr18Si2 and Cr25 in China and AISI442, 443, and 446 in the United States. This type of steel has good oxidation resistance. 442 is continuously used in the atmosphere, the upper limit temperature is 1035°C, and the maximum temperature for continuous use is 980°C. 446 has better oxidation resistance.

High-purity ferritic stainless steel

Such steels contain very low carbon, and nitrogen; high chromium, molybdenum, titanium, niobium, and other elements. Such as Chinas 00Cr17Mo, 00Cr18Mo2, 00Cr26Mol, 00Cr30Mo2 abroad 18-2, Cr26Mol, 25Cr-5Ni-4Mo-Nb, MoNiT, Al29-4, Al29-4-2. These steels have good mechanical properties (especially toughness), weldability, resistance to intergranular corrosion, pitting corrosion, crevice corrosion, and excellent resistance to stress corrosion cracking. For example, 18-2 has good corrosion resistance in nitric acid, acetic acid, and NaOH. The pitting resistance in 3% NaCl and FeCl3 is equivalent to or exceeds 18-8 austenitic steel, and the SCC resistance is far more than 18-8 steel. 26CrMo steel is resistant to corrosion in many media, especially organic acids, oxidizing acids, and strong bases. Good pitting resistance in strong chloride media. No stress corrosion cracking occurs in chloride, hydrogen sulfide, excess sulfuric acid, and strong alkali. 30Cr-2Mo has higher pitting corrosion resistance and crevice corrosion resistance while maintaining stress corrosion resistance. Add a small amount of nickel steel to improve performance in reducing acid.