Why does stainless steel part rust?

Why does stainless steel part rust? When brown rust spots (spots) appear on the surface of stainless steel fasteners, people are surprised: "Stainless steel does not rust, and rust is not stainless steel. It may be a problem with the steel." In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will rust under certain conditions.

Stainless steel has the ability to resist atmospheric oxidation-that is, non-rust, and it also has the ability to corrode in acid, alkali, and salt media-that is, corrosion resistance. However, the size of its corrosion resistance varies with the chemical composition of the steel itself, the state of protection, the use conditions and the type of environmental media. Such as 304 steel parts, in a dry and clean atmosphere, has absolutely excellent anti-corrosion ability, but when it is moved to the beach area, it will quickly rust in the sea fog containing a lot of salt; while 316 steel pipe is performance good. Therefore, it is not any kind of stainless steel, which can resist corrosion and rust in any environment.