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 Why does stainless steel rust?
Why does stainless steel rust? People generally think that stainless steel is not rusting, and rust is not stainless 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 - rust, but also has the ability to corrode in acids, alkalis, and salts - corrosion resistance. However, the amount of corrosion resistance varies with the chemical composition of the steel itself, the state of protection, the conditions of use, and the type of environmental medium.
Why does stainless steel rust
For example, the 304 steel pipe has absolutely excellent rust resistance in a dry and clean atmosphere, but it is moved to the coastal area, and in the sea fog containing a large amount of salt, it will soon rust; while the 316 steel pipe is in It performs well in this environment. Therefore, it is not any kind of stainless steel that is resistant to corrosion and rust in any environment.
Stainless steel is a very thin and strong and stable chromium-rich oxide film (protective film) formed on the surface to prevent the oxygen atoms from continuing to infiltrate and continue to oxidize, thereby obtaining the ability to resist rust. Once for some reason, the film is constantly destroyed, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will be continuously separated, forming loose iron oxide, and the metal surface will be continuously rusted.
There are many forms of such surface film damage, and the following are common in daily life:
1. The surface of stainless steel contains dust or other metal particles attached to other metal elements. In humid air, the condensed water between the attached material and the stainless steel connects the two into a micro battery, triggering an electrochemical reaction. The protective film is damaged, which is called electrochemical corrosion.
2, the surface of the stainless steel adheres to the organic juice (such as melon, noodle soup, wolfberry, etc.), in the case of water and oxygen, constitutes an organic acid, and the organic acid corrodes the metal surface for a long time.
3. The surface of the stainless steel adheres to acid, alkali and salt substances (such as alkali water and lime water splashing on the wall), causing local corrosion.
4. In polluted air (such as the atmosphere containing a large amount of sulfide, carbon oxide, nitrogen oxide), in the case of condensed water, sulfuric acid, nitric acid, acetic acid liquid point is formed, causing chemical corrosion.
To ensure that the metal surface is permanently bright and not rusted, we should:
1) The surface of the decorative stainless steel must be cleaned and scrubbed frequently to remove the deposits and eliminate external factors that cause corrosion.
2) Choose stainless steel that meets the surrounding environment; for example, 316 is resistant to seawater corrosion.
3) Some stainless steel tubes in the market do not meet the corresponding national standards and cannot meet the material requirements. This requires careful selection of products from reputable manufacturers.
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