Why does stainless steel rust? When brown rust spots (spots) appear on the white surface of stainless steel, people are surprised: "Stainless steel is not rusty, rust is not stainless steel, it may be a problem with 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, stainless, and colleagues also have the ability to resist corrosion in media containing acids, alkalis, and salts-that is, corrosion resistance. However, the size of its anti-corrosion ability changes with the chemical composition of the steel itself, the state of protection, use conditions and the type of environmental medium. Such as 304 steel pipe, in the dry and clean atmosphere, it has absolutely excellent corrosion resistance, but it is moved to the seaside area in a sea fog containing a lot of salt. It will soon rust; and 316 steel pipe performs well. Therefore, it is not any kind of stainless steel, which is resistant to corrosion and rust in any environment.
Stainless steel is based on its surface to form an extremely thin, strong, dense and stable chromium-rich oxide film (protective film), to prevent oxygen atoms from infiltrating and oxidizing, and to obtain the ability to resist rust. Once there is a reason. This kind of film has been continuously damaged, and the oxygen atoms in the air or liquid will continue to infiltrate and the iron atoms in the living metal will continue to separate out, forming loose iron oxide, and the metal surface will be continuously rusted. There are many forms of damage to this surface film, and the following are common in daily life:
1. The surface of the stainless steel contains dust or other metal particles containing other metal elements. In the humid air, the condensate between the attachment and the stainless steel connects the two into a micro battery, which initiates electrochemistry Reaction, the protective film is damaged, called electrochemical corrosion.
2. Organic matter juice (such as melon and vegetable, noodle soup, sputum, etc.) adheres to the surface of the stainless steel. In the presence of water and oxygen, it forms an organic acid, and the organic acid will corrode the metal surface for a long time.
3. Acid, alkali and salt substances adhere to the surface of the stainless steel (such as alkali water and lime water splashing on the decoration wall), causing local corrosion.
4. In contaminated air (such as an atmosphere containing a large amount of sulfides, carbon oxides, and nitrogen oxides), when it encounters condensed water, it forms sulfuric acid, nitric acid, and acetic acid liquid spots, causing chemical corrosion.
To ensure that the metal surface is permanently bright and not rusted, we recommend:
1) The surface of the decorative stainless steel must be cleaned and scrubbed frequently to remove attachments and eliminate external factors that cause rust.
2) 316 stainless steel should be used in the seaside area, which can resist seawater corrosion.
3) The chemical composition of some stainless steel pipes on the market can not meet the corresponding national standards, and can not meet the requirements of 304 materials. Therefore, it will also cause rust, which requires users to carefully select products from reputable manufacturers.
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