Stainless Steels

Stainless steels are corrosion-resistant steels that contain at least 10.5% chromium. Chromium is unique in that it forms a passive layer on the steel surface that provides protection from corrosion. There are basically five types of stainless steels: austenitic, ferritic, duplex, martensitic, and precipitation hardening steels. These five types of stainless steel have a somewhat simplified classification system as follows:

Austenitic stainless steels with low nickel 2xx series

Austenitic stainless steels 3xx series

Ferritic stainless steels 4xx series

Duplex stainless steel 329

Martensitic stainless steels 4xx series

Precipitation strengthening stainless steels 6xx (xx-x PH)

The classification system is different for the stainless steels than the system for SAE/AISI low-alloy steels in that the last two digits (xx) do not represent the carbon content and have no particular compositional  meaning. Unfortunately, the classification system has some confusion with the ferritic and martensitic stainless steels both of the 4xx series. The 2xx series of austenitic stainless steels were developed during the 1950s when nickel became scarce. In these steels, manganese and nitrogen were substituted for the lower nickel level in order to maintain strength.

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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