Stainless steel tools has resistance to atmospheric oxidation, namely rustless property, and resistance to corrosion in medium containing acid, base and salt, that is corrosion resistance. A thin, solid, dense and stable chromium-rich oxidation film (protective film) is formed on the surface of stainless steel. This film prevents further permeate and oxidation of oxygen atom, making the stainless steel of corrosion resistance. Once this film is continuously destroyed for one reason or another, the oxygen atoms in the air or liquid will gradually penetrate into the metal. Then the iron atoms will separate out gradually, forming loose iron oxide. So the metal surface is constantly corroded. The form of such damage to the surface film is various, and the following are the common types in daily life:
