When brown rust spots (spots) appeared on the surface of the 304 stainless steel butterfly valve, people were amazed: “Stainless steel will not rust, rust is not stainless steel, it may be a problem with the steel”. In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will also rust under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation, that is, rust resistance, and also has the ability to resist corrosion in media containing acids, alkalis, and salts, that is, corrosion resistance. However, the corrosion resistance of stainless steel varies with the chemical composition of the steel itself, the mutual state, the conditions of use and the type of environmental media.
304 stainless steel butterfly valve has excellent corrosion resistance in a dry and clean atmosphere, but 304 stainless steel butterfly valve will rust quickly in seaside areas and sea fog containing a lot of salt.
Stainless steel is a very thin, firm and stable chromium-rich oxide film (protective film) formed on its surface to prevent oxygen atoms from continuing to infiltrate and continue to oxidize, so as to obtain the ability to resist corrosion.
Once for some reason, this protective film is constantly damaged, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be continuously affected. Therefore, the stainless steel butterfly valve loses its original corrosion resistance.