What would cause stainless steel sphere to rust? (Ⅰ)

When there are brown rust spots appeared on the surface of stainless steel pipes, people were surprised: “Stainless steel is never rusty, products that are rust is not made from stainless steel, there may be some problems with the stainless steel.” In fact, it is a wrong view for lack of knowledge about stainless steel. Stainless steel sphere and even stainless steel will be rusty under some circumstances.

Stainless steel has the ability to resist atmospheric oxidation–that is, stainless and also the ability to resist damage from media containing acids, alkalis, and salts–that is, corrosion resistance. However, the ability to resist corrosion depends on chemical composition of the steel itself and the environment. For example, 304 steel pipe has absolutely excellent rust resistance in a dry and clean atmosphere, while it will be rusted quickly when it is moved to the seashore area where sea fog containing a large amount of salt. However, 316 steel pipe still has a good performance under such situation. Therefore, not every stainless steel can remain corrosion resistance and rust resistance under all circumstance.