PASSIVATION:
Passivation is "the removal of free iron particles or iron compounds from the stainless steel surface by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination."

In lay terms, the passivation process removes "free iron" contamination left behind on the surface of the stainless steel from machining and fabricating. These contaminants are potential corrosion sites that result in premature corrosion and ultimately result in deterioration of the component if not removed. In addition, the passivation process facilitates the formation of a thin, transparent oxide film that protects the stainless steel from selective oxidation (corrosion).