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Why does stainless steel also rust?

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2022-08-12 09:25

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When brown rust spots (spots) appear on the surface of stainless steel pipes, people are amazed: "Stainless steel does not rust, and if it rusts, it is not stainless steel, and there 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 it also has the ability to corrode in media containing acids, alkalis, and salts—that is, corrosion resistance. However, the size of its anti-corrosion ability varies with the chemical composition of its steel itself, the state of mutual addition, the conditions of use and the type of environmental media. For example, 304 stainless steel plate has absolutely excellent anti-corrosion ability in a dry and clean atmosphere, but if it is moved to the seaside area, it will rust soon in the sea fog containing a lot of salt; and 321 stainless steel plate Steel pipes are doing well. Therefore, it is not any kind of stainless steel that can resist corrosion and rust in any environment.
The stainless steel plate is a very thin, firm and stable chromium-rich oxide film formed on its surface, which prevents the continuous infiltration and oxidation of oxygen atoms, and obtains the ability to resist rust. Once the film is damaged continuously for some reason, the oxygen atoms in the air or liquid will continue to infiltrate or the iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be continuously corroded.

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