Contrarily to what people generally believe, chrome is a very chemically reactive metal that oxidizes easily, but it’s oxide forms a transparent and protective layer. Alloyed to iron and nickel, it causes the formation of an oxided surface component capable of reducing or stopping corrosion.
Chrome and nickel oxide this way :
4 Cr + 3 O2 -> 2 Cr2O3
2 Ni + O2 -> 2 NiO
Stainless is a misleading and inappropriate term
There is a variety of stainless steels, and the type may be difficult to choose. Each stainless steel reacts differently to its environment. The type is often represented by the mass percentage of nickel and chrome. An inox 18\10, used in cutlery and cooking in general, contains 18% of its mass in chrome and 10% in nickel. This designation is insufficient since it does not refer to its metallurgical structure.
The chrome content is always at least 12%. Other alloying elements, for most “noble” metals such as nickel, molybdenum, copper or brass, improve its chemical resistance mostly in non oxidant environments.