Why does stainless steel rust? When the stainless steel plate surface brown rust spots (points), people are surprised: that "stainless steel is not rust, rust is not stainless steel, may be a problem with the steel". In fact, this is a lack of understanding of stainless steel, a one-sided view of the error. 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 its steel itself, plus mutual state, use conditions and the type of environmental media and change. Such as 304 stainless steel plate, in the dry clean atmosphere, has excellent corrosion resistance, but it will be moved to the seaside area, in the sea spray containing a large amount of salt, will soon rust, and 316 stainless steel plate is 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 the continued penetration of oxygen atoms, continue to oxidise, and obtain the ability to resist rust and corrosion. Once there is some reason, this film has been constantly destroyed, air or liquid oxygen atoms will continue to penetrate or metal iron atoms continue to precipitate out, the formation of loose iron oxide, the metal surface is also subject to constant rust.
