Stainless steel relies on the formation of an extremely thin, strong, fine, and stable chromium-rich oxide film (protective film) on its surface to prevent oxygen atoms from continuing to penetrate and oxidize, thereby obtaining the ability to resist corrosion. Once this film is continuously damaged for some reason, oxygen atoms in the air or liquid will continue to penetrate or iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be constantly damaged. rust. There are many forms of damage to this surface film.
Stainless steel has the ability to resist atmospheric oxidation-that is, it is rustless. It also has the ability to resist corrosion in media containing acid, alkali and salt, that is, corrosion resistance. However, its corrosion resistance changes with the chemical composition of the steel itself, its mutual state, usage conditions and environmental medium types. For example, 304 stainless steel pipes have absolutely excellent corrosion resistance in a dry and clean atmosphere. But if it is moved to a coastal area, it will soon get rusty in the sea fog containing a large amount of salt. Therefore, not any kind of stainless steel can be corrosion-resistant and rust-free at any time. All of the above situations can cause damage to the protective film on the stainless steel surface and cause corrosion.
