Why is stainless steel rusty? When the stainless steel pipe surface brown rust spots (spots), people are surprised: that "stainless steel is not rusty, rust is not stainless steel, may be steel problems." In fact, this is a one-sided misconception about the lack of stainless steel. Stainless steel will rust under certain conditions. Stainless steel has the ability to resist atmospheric oxidation - - that is, stainless, but also in acid, alkali, salt in the medium of corrosion resistance - - corrosion resistance. However, the corrosion resistance of the steel varies with its chemical composition, additive state, service condition and environmental medium type. For example, 304 steel pipe has absolutely excellent corrosion resistance in dry and clean atmosphere, but it will soon rust when moved to the coastal area in a sea fog containing a lot of salt; 316 steel pipe is good performance. Therefore, not any stainless steel can be corroded without rust in any environment.
Stainless steel is formed by its surface of a very thin and solid fine stable chromium-rich oxide film (protective film), to prevent oxygen atoms continue to penetrate, continue to oxidize, 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 infiltrate or iron atoms in the metal will continue to separate out, forming a loose iron oxide, metal surface will be constantly corroded.