Back to home Page S.Inox Spa - Austenitic Stainless Steels Austenitic stainless steels AISI 304 AISI 321 AISI 316 AISI 316Ti AISI 309 AISI 310 Stainless steels are a family of materials with one common feature. These steels are protected by a surface film of chromium oxide, created by the chromium contained in its alloy and by the oxygen of the atmosphere. Stainless steels do not require any additional surface protection against corrosion. In the event that the surface is damaged, the film self-builds immediately in the presence of oxygen. Austenitic stainless steels Steels consisting of chromium-nickel alloys, with chromium between 17 and 26% and nickel between 7 and 22%. It is a steel containing Ni and Cr in such a percentage as to preserve the austenitic structure even at room temperature. It is classified according to the percentage of Ni and Cr (see table); in the ASTM classification constitutes the 3XX series. The basic composition of austenitic stainless steel is 18% Cr and 8% Ni, coded in 18/8. A percentage of 2-3% of molybdenum ensures better resistance to corrosion (18/8/3 steel). The carbon content is low (0.08% max of C), but there are also mild austenitic stainless steels (0.03% of C max). Austenitic stainless steel can be stabilized with titanium or niobium to avoid a form of corrosion in the weld area (see below for the weaknesses of this type of steel). Considering the considerable percentage of high-quality components (Ni, Cr, Ti, Nb, Ta), austenitic stainless steels are among the most expensive among the commonly used steels. The fundamental properties are: - excellent resistance to corrosion; - ease of cleaning and excellent hygienic coefficient; - easy to work, forge and weld; - unbreakable if cold worked and not by heat treatment; - slightly magnetic in the raw state, (austenitic steels can generate during the cold transformations of the martensitic phase patches that present a certain ferromagnetism) in a condition of total annealing it does not magnetize. Their austenitic structure (with cfc crystal) makes them immune from the ductile-brittle transition (which manifests itself instead with the ferritic structure, ccc crystal), therefore they retain their toughness up to cryogenic temperatures (liquid He). The grain size, significantly higher than that of ferritic construction steels, makes them resistant to creep; consequently among the steels for construction of pressure vessels, they are those that can be used at the highest temperatures (600 ° C). Since austenite is paramagnetic, these steels can be easily recognized by having calibrated permanent magnets. The uses of these steels are vast: pots and domestic services, architectural finishes, abattoirs, breweries, beverage cans and food products; liquefied gas tanks, heat exchangers, pollution control and smoke extraction devices, industrial autoclaves. Their resistance to most aggressive chemicals also makes them very popular in the chemical industry. However, austenitic stainless steels suffer from some limitations: - the maximum temperature at which they can be treated is 925 ° C; - at low temperature the corrosion resistance decreases drastically: the acids break the oxide film and this causes generic corrosion in these steels; - in the cracks and in the protected areas the quantity of oxygen may not be sufficient to preserve the oxide film, with consequent crevice corrosion; - the halide ions, especially the anion (Cl-), break the passivating film on austenitic stainless steels and cause the so-called pitting corrosion, defined in jargon as pitting corrosion. Another effect of chlorine is SCC (stress corrosion cracking). The only recommended heat treatment for this class of steels is that of solubilization of C at 1050 ° C, with rapid cooling (to avoid the permanence in the area between 800 and 400 ° C, where the precipitation of Cr carbides can occur. ). Main Menu Home Headquarters and Contacts Download Catalog Products Terms of Sale Success story Automation Austenitic stainless steels Photogallery English Version Products menu Pipes Long Products Sheet metal Fittings Valves Flanges Press Inoxpres Networks St - Tele Lam For Screws Ogiva fittings Professional Chemical Products Accessories menu Accessories Gel Soldering Material Fittings And Smoke Pipes Gaskets and Elastomers Pipes pressures S.INOX Spa - Via San Francesco D'Assisi 58/60, 25039 Travagliato (BS) - Tel: +39 030 68 62 111 - Fax: +39 030 68 64 817 - info@essepuntoinox.com VAT number and CF 02098980986 - Share capital IV 1,000,000.00 Back to Top © S.Inox Spa 2018