>1. What happen if we grind on outer >surface i.e. to this layer? If you do mechanical damage to the passive layer, it is gone and the stainless is susceptible to corrosion. >2. After grinding as this layer removed, shall it form it >again? if yes how? Mostly you form the layer the same way you did the first time, by passivating the part. It depends on the grade of stainless somewhat, 300 series stainlesses are self-passivating to a degree, though a passivation treatment is still better. >3. what is the thickness of this layer? Depending on the passivation method used, typically 20-30 angstroms. >4. If this layer form agai automatically, is it effect the >amount of chromium in the steel?(reduction of chromium in >%age) Stainless grades with higher chromium content are better at forming a passive layer. Passivation and the passive layer only involves the very surface, the alloy composition beneath remains unchanged.