All stainless steels have a high resistance to corrosion. This resistance to attack is due to the naturally occurring chromium-rich oxide film formed on the surface of the steel. Although extremely thin, this invisible, inert 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.
Fig. 1 - In any normal oxidising environment a protective coating of passive chromium rich oxide film is automatically formed on stainless steel.
Fig. 2 - When scratched, damaged or machined this protective film is denuded exposing the steel to the atmosphere.
Fig. 3 - The protective coating is quickly restored through the rapid self-repairing quality of the chromium rich film.