Causes of rust attack on stainless steel
Stainless steel is not simple rust and has a lot of contact with stainless steel components. In addition to iron, stainless steel contains chromium, nickel, aluminum, silicon and so on. The chromium content of stainless steel in general is not less than 12%, high or even 18%. When chromium and other elements are added to the steel, the function of the steel can be changed, for example, the molecule structure of the example steel is more uniform, and a dense oxide protective film is easily formed on the surface of the steel, which greatly improves the corrosion resistance of the stainless steel. So stainless steel can resist fire, water, acid, alkali and corrosion of various solutions to it, without rust. Scientists have found that the more uniform the steel's internal structure, the more closely the various components are linked, the more difficult it is to invade the corrosive material, and the more oxide-coated the surface, just like putting armor on the steel, the less rusty it is. But stainless steel also rusts.
Stainless steel is a very thin and stable chromium-rich oxide film (protective film) formed by its appearance, which can prevent oxygen atoms from continuously entering and oxidizing, and obtain the ability to resist corrosion. Once for some reason, the film is constantly destroyed, oxygen atoms in the air or liquid will continue to enter or iron atoms in the metal will continue to separate out, forming a loose iron oxide, metal surface will be constantly corroded. There are many ways to destroy the outer membrane.
1. The stainless steel surface contains dust containing other metal elements or heterogeneous metal particles of the attachment, in the humid air, the attachment and the condensate between stainless steel, the two connected into a micro-battery, triggered the electrochemical reaction, the protective film was damaged, known as electrochemical corrosion.
2. The stainless steel surface is adhered with organic juice (such as melon, vegetable, noodle soup, phlegm, etc.), in the presence of water and oxygen, organic acids form, long-term corrosion of the metal surface organic acids.
3. The stainless steel surface contains acid, alkali and salt substances (such as alkaline water and lime water splashing on decorative walls) which cause partial corrosion.
4. In the polluted air (such as atmosphere containing a large number of sulfides, carbon monoxide, nitric oxide), when encountering condensate, it forms sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.
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