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Stainless steels are those alloys of iron and chromium, with or without other elements, containing at least 11% chromium. This is the minimum amount of chromium necessary to form a stable, passive chromium oxide film. It is this film that is the basis for the corrosion resistance of all stainless, and most nickel-base, corrosion-resistant alloys.
There are six basic classifications of stainless steels: ferritic, martensitic, martensitic age hardening, duplex austenitic–ferritic, and austenitic. The most commonly produced of these are the ferritics 409 for automotive applications and 430 for corrosion-resistant /decorative uses, the martensitic grade 410, and the age-hardening martensitic 17-4PH . Of the austenitic–ferritic duplex grades, alloy 2205 is the most broadly available. The two most used austenitic stainless grades are 304L and 316L. A number of ‘‘superaustenitics’’ use nitrogen to maintain an austenitic structure with relatively high molybdenum, some 6%, and moderate nickel, 18–25%. Of the higher nickel grades alloys 825 and 20 are used for sulfuric acid and general chemical processing. The most commonly used of the very high nickel alloys is C-276. The austenitic stainless steels form a continuum with the nickel-base heatand corrosion-resistant alloys. They are distinguished on the basis of nickel content by arbitrary or commercial definitions. There is no recognized metallurgical definition of where stainless ends and nickel base begins.
Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright 2006 by John Wiley & Sons, Inc.
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