Stainless steel is a very thin layer formed on the surface of the solid stability of dense chromium-rich oxide film (protective film), to prevent the infiltration of oxygen atoms, to oxidation, and the ability to obtain anti-corrosion.

If for some reason, this film was constantly undermined, air or liquid oxygen atoms will continue to infiltrate or metal atoms of iron to keep out from it, the loose formation of iron oxide, metal surface is subject to constant corrosion.