Stainless steel is a generic term for a group of corrosion resistant steels containing a minimum of 10.5% of chromium. Varying additions of nickel, molybdenum, titanium, niobium and other elements may also be present.
All stainless steels have a high resistance to corrosion. This remarkable resistance to attack is due to the naturally occurring chromium-rich oxide film present on the surface of the steel. Although extremely thin, this invisible, inert film and therefore passive film is tightly adherent to the metal and extremely protective in a wide range of corrosive media. The film is rapidly self-repairing in the presence of oxygen, and damage by abrasion, cutting or machining is quickly repaired (see Figures 1, 2 and 3 below).
There are five basic categories of stainless steel: austenitic, ferritic, duplex, martensitic and precipitation hardening.