Stainless steel passivation is a chemical treatment basically indispensable. 
Thanks to this process, indeed, the stainless steel is guaranteed an excellent surface protection, making it particularly resistant to corrosion, due to the action of water, air and other chemical substances.
The passivation treatment facilitates a natural process that requires the formation of a protective film on stainless steel, which prevents the progress of the metal normal oxidation, hence its corrosion.

Complying with standard QQ-P-35, ASTM 2700B