Stainless actually forms a very thin layer of chromium oxide on the surface. This layer can still be polished, but prevents further oxidation.

Though this layer will not form a protective barrier if chromium/iron steel is submerged in water, and it will rust in this state.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris