Why are stainless steel passive?

Answer 1

stainless steels are specials grades of steel with a minimum of 10% chromium. tool steels also contain chromium but they differ from the fact that the stainless steels have very low percentage of carbon. presence of carbon is a negative factor because chromium has high affinity to carbon and oxygen. chromium carbide is undesirable , only chromium oxide is necessary as it forms the thin layer referred to as the passive film. chromic oxide is very stable oxide that forms spontaneously on stainless steels upon exposure to air. this thin layer must be uniform, continuous, and free from defects for corrosion resistance. the passive film hence formed should not be disturbed in any case else corrosion becomes inevitable.there many processes like pickling, passivating,mechanical and electrochemical cleaning performed to remove any rust so that the passive film is uniform to prevent corrosion.