Stainless steel is a generic term for a family of corrosion resistant alloy steels containing 10.5% or more chromium.
all stainless steels can be divided into five basic categories:
These are named according to the microstructure inherent in each steel group (a function of the primary alloying elements).
The basic composition of austenitic stainless steels is 18% chromium and 8% nickel. This enhances their corrosion resistance and modifies the structure from ferritic to austenitic .Austenitic grades are the most commonly used stainless steels They are not hardenable by heat treatment. Austenitic stainless steels are non-magnetic.
FERRITIC stainless steels are magnetic, have a low carbon content and contain chromium as the main alloying element, typically between 13% and 17%.They are not hardenable by heat treatment.
MARTENSITIC stainless steels are magnetic, containing typically 12% chromium with a higher carbon content compared to other stainless steels . They are hardenable by quenching and tempering like plain carbon steels.
These are stainless steels containing relatively high chromium (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%) They have a mixed structure of austenite and ferrite.DUPLEX stainless steels are used where combinations of higher strength and corrosion resistance are needed. They are not hardenable by heat treatment.
Precipitation hardening stainless steels are chromium and nickel containing steels that provide an optimum combination of the properties of martensitic and austenitic grades. Precipitation hardening stainless steels, like the martensitic types, can be strengthened (ie hardened) by heat treatment and they also have the corrosion resistance of austenitic stainless steel.