Stainless steel is not easy to rust with the composition of stainless steel has a great relationship. In addition to iron in the composition of stainless steel, there are chromium, nickel, aluminum, silicon and so on. General stainless steel containing chromium is generally not less than 12%, and the high even reached 18%. After the addition of chromium and other elements in steel, it can change the performance of steel, such as example of the molecular structure of steel is more uniform, the surface of the steel is more likely to generate a layer of dense oxide protective film, etc., which greatly improves the ability of stainless steel corrosion resistance. So stainless steel can resist fire, water, acid, alkali and various solutions to its corrosion, not rust. Scientists have found that the internal structure of steel, the more uniform, the various components are linked more closely, the corrosive invasion of the more difficult, coupled with the surface and attached to a layer of oxide protective film, as if the steel to wear armor, naturally, it is not easy to rust.
Why does stainless steel rust? When the surface of the stainless steel tube appears brown rust spots (points), people are surprised: that "stainless steel is not rust, rust is not stainless steel, may be a problem with the quality of steel". In fact, this is a lack of understanding of stainless steel a one-sided wrong view. Stainless steel will rust under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation --- that is, stainless steel, but also in the medium containing acids, alkalis, salts, and the ability to corrode --- that is, corrosion resistance. But the size of its corrosion resistance is with the chemical composition of the steel itself, plus mutual state, conditions of use and the type of environmental media and change. Such as 304 steel pipe, in the dry and clean atmosphere, there is absolutely excellent corrosion resistance, but it will be moved to the seaside areas, in the sea spray containing a large amount of salt, will soon rust; and 316 steel pipe is a good performance. Therefore, not any kind of stainless steel, in any environment can resist corrosion, not rust.
Stainless steel is relying on its surface to form a layer of very thin and solid dense stable chromium-rich oxide film (protective film), preventing oxygen atoms continue to penetrate, continue to oxidize, and obtain the ability to resist rust and corrosion. Once there is some reason, this film has been constantly damaged, oxygen in the air or liquid will continue to penetrate or metal iron atoms continue to separate out, the formation of loose iron oxide, the surface of the metal is also subjected to constant corrosion. This surface film is damaged in many forms, daily life in the following kinds:
1. Stainless steel surface deposits containing other metal elements of dust or foreign metal particles of the adherents, in the humid air, the adherents and stainless steel condensation, will be connected to a microcell, triggered by an electrochemical reaction, the protective film is damaged, known as galvanic corrosion.
2. Stainless steel surface adhering to organic sap (such as vegetables, noodle soup, phlegm, etc.), in the presence of water and oxygen, constituting an organic acid, a long period of time, the corrosion of organic acids on the surface of the metal.
3. Stainless steel surface adhesion containing acid, alkali, salt substances (such as alkali water, lime splash decoration wall), causing local corrosion.
4. In the polluted air (such as the atmosphere containing a large number of sulfides, carbon oxides, nitrogen oxides), condensation, the formation of sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.