Chromindholdet er 12 procent til 30 procent, og det krops-centrerede kubiske gitter af ferrit bruges som matrixstruktur af rustfrit stål ved høj temperatur og normal temperatur. Denne type stål indeholder generelt ikke nikkel, og nogle indeholder en lille mængde molybdæn, titanium eller niobium og andre elementer, og har god oxidationsbestandighed, korrosionsbestandighed og modstandsdygtighed over for kloridkorrosionsrevner. Ifølge chromindholdet kan ferritisk rustfrit stål opdeles i tre kategorier: lavt chrom, medium chrom og højt chrom. Alt efter stålets renhed, især indholdet af kulstof- og nitrogenurenheder, kan det opdeles i almindeligt ferritisk rustfrit stål og ultra-rent ferritisk rustfrit stål. . Almindelig ferritisk rustfrit stål har mangler såsom skørhed ved lav temperatur og stuetemperatur, hakfølsomhed, høj intergranulær korrosionstendens og dårlig svejsbarhed. Selvom denne type stål er udviklet tidligere, har dens industrielle anvendelse været meget begrænset. Disse mangler ved almindeligt ferritisk rustfrit stål er relateret til stålets renhed, især det høje indhold af interstitielle elementer såsom kulstof og nitrogen i stålet. Så længe kulstof og nitrogen i stålet er tilstrækkeligt lavt, for eksempel ikke mere end 15010 til 25010-6, kan ovenstående ulemper grundlæggende overvindes. Efter 1970'erne er der på grund af udviklingen af smelteteknologi, især vakuummetallurgi og sekundær raffineringsproces, blevet fremstillet ferritisk rustfrit stål med høj renhed med kulstof plus nitrogen Mindre end eller lig med 150 250 10-6, hvilket gør denne type stål industrielt opnåelig. alment benyttet.
Generelt kan det opdeles i to kategorier: almindeligt ferritisk rustfrit stål og ferritisk rustfrit stål med høj-renhed.
Almindelig ferrit
Such steels include low, medium and high chromium content. Low chromium ferritic stainless steel contains about 11 percent to 14 percent 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 percent to 19 percent , 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 percent to 30 percent 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 degree , and the maximum temperature for continuous use is 980 degree . 446 has better antioxidant properties.
Ferrit med høj renhed
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 percent 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.