What is the Ferritic Stainless Steel?
Ferritic stainless steel (400 series) has a chromium content of 15% to 30% and has a body-centered cubic crystal structure. This type of steel generally does not contain nickel, and sometimes contains a small amount of Mo, Ti, Nb and other elements. This type of steel has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, and excellent stress corrosion resistance. , Parts corroded by water vapor, water and oxidizing acid. With many unique features and advantages, it has been proven that ferritic stainless steel is an excellent alternative material in many applications where austenitic stainless steel (300 series) was originally considered only, and 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.
Generally, it can be divided into two categories: ordinary ferritic stainless steel and high-purity ferritic stainless steel.
Folded Ordinary Ferrite
Such steels include low, medium and high chromium content. Low chromium ferritic stainless steel contains about 11% to 14% chromium, such as 00Cr12 and 0Cr13Al in China. AISI400, 405, 406MF-2 in the United States (see table). This type of steel has 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 petroleum refining towers, tank linings, steam turbine blades, high temperature sulfur corrosion resistance devices, etc. 400 is used for home and office appliances, etc. 409 is used in automobile exhaust muffler system devices and cold and warm water pipes, etc. Medium chromium ferritic stainless steel, the chromium content is 14%~19%, such as 1Cr17 and 1Cr17Mo in China. AISI429, 430, 433, 434, 435, 436, 439 in 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 poor ductility. 430 is used as building decoration, automobile decoration, kitchen equipment, gas burner and parts of nitric acid industrial equipment, etc. 434 is used for exterior decoration of automobiles, buildings. 439 is used as a hose for gas water heaters, coal and gas pipelines, etc. High chromium ferritic stainless steels contain 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 used continuously in the atmosphere, the upper limit temperature is 1035℃, and the maximum temperature for continuous use is 980℃. 446 has better antioxidant properties.
Folded high-purity ferrite
This type of steel contains extremely low carbon, nitrogen; high chromium, molybdenum, titanium, niobium and other elements. Such as China's 00Cr17Mo, 00Cr18Mo2, 00Cr26Mol, 00Cr30Mo2 foreign 18-2, Cr26Mol, 25Cr-5Ni-4Mo-Nb, MoNiT, Al29-4, Al29-4-2. This type of steel has good mechanical properties (especially toughness), weldability, intergranular corrosion resistance, pitting corrosion resistance, crevice corrosion resistance, and excellent stress corrosion cracking resistance. For example, 18-2 has good corrosion resistance in nitric acid, acetic acid and NaOH. In 3%NaCl and FeCl3, its pitting corrosion resistance is equivalent to or exceeds that of 18-8 austenitic steel, and its SCC resistance is much higher than that of 18-8 steel. 26CrMo steel is resistant to corrosion in many media, especially in organic acids, oxidizing acids, and strong alkalis. Good pitting resistance in strong chloride media. Stress corrosion cracking does not occur in chloride, hydrogen sulfide, excessive sulfuric acid and strong alkali. 30Cr-2Mo has higher resistance to pitting and crevice corrosion while maintaining stress corrosion resistance. Steel with a small amount of nickel added to improve performance in reducing acids.
