Good article recommendation - "Does stainless steel rust?"”

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Let’s first talk about why stainless steel is not easy to rust, and then let’s talk about why stainless steel can also rust. The fact that stainless steel is not easy to rust has a lot to do with the composition of stainless steel. In addition to iron, stainless steel also contains chromium, nickel, aluminum, silicon, etc. The chromium content of general stainless steel is generally not less than 12%, and the highest chromium content can even reach 18%. Adding chromium and other elements to steel can change the properties of the steel. For example, the molecular structure of the steel will be more uniform, and a dense oxide protective film will be more easily formed on the surface of the steel. * * Improve the corrosion resistance of stainless steel. Therefore, stainless steel can resist corrosion by fire, water, acid, alkali and various solutions, and will not rust. Scientists have found that the more uniform the internal structure of steel, the closer the various components are connected, and the more difficult it is for corrosion to invade. In addition, there is a protective oxide film attached to the surface, just like putting armor on steel, which naturally makes it less likely to rust. Why does stainless steel also rust? People are surprised when brown rust spots (dots) appear on the surface of stainless steel pipes: It is believed that "stainless steel does not rust. If it rusts, it is no longer stainless steel. There may be a problem with the steel." In fact, this is a one-sided wrong view due to lack of understanding of stainless steel. Stainless steel can also rust under certain conditions. Stainless steel has the ability to resist atmospheric oxidation---that is, stainless steel, and also has the ability to corrode 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 additive state, usage conditions and environmental medium types. For example, 304 steel pipes have absolutely excellent corrosion resistance in a dry and clean atmosphere. But if they are moved to a coastal area, they will soon get rusty in the sea fog containing a large amount of salt. ； The 316 steel pipe performed well. Therefore, not any kind of stainless steel can resist corrosion and rust in any environment. 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 the continued penetration and oxidation of oxygen atoms, thereby obtaining the ability to resist rust. 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 continuously corroded. There are many ways in which this surface film is damaged. The following are the common ones in daily life:: 1. Dust containing other metal elements or attachments of heterogeneous metal particles accumulate on the surface of stainless steel. In humid air, the condensed water between the attachments and the stainless steel connects the two into a micro-battery, triggering an electrochemical reaction and destroying the protective film, which is called electrochemical corrosion. 2. Organic juices (such as vegetables, noodle soup, phlegm, etc.) adhere to the surface of stainless steel. In the presence of water and oxygen, they form organic acids. For a long time, the organic acids will corrode the metal surface. 3. The surface of stainless steel contains acids, alkalis, and salts (such as alkaline water and lime water splashed on walls), causing local corrosion. 4. In polluted air (such as an atmosphere containing a large amount of sulfides, carbon oxides, and nitrogen oxides), when encountering condensed water, sulfuric acid, nitric acid, and acetic acid liquid points will form, causing chemical corrosion.