Stainless Steel Passivation
What is Passivation?
Passivation of stainless steel is not electroplating, it is a non-electrical process whereby the free iron is chemically removed from the surface of stainless steel. The passivation process prevents the formation of possible corrosion sites and the development of tightly adhering oxides on stainless steel. Passivation removes exogenous iron or iron compounds from the surface of a stainless steel by means of a chemical dissolution that will remove the surface contamination but will not significantly affect the stainless steel itself.
Stainless Steel Passivation Process Overview
Passivation is the process by which a stainless steel will spontaneously form a chemically inactive surface when exposed to air or other oxygen-containing environments. The 300 series stainless steel alloys are generally preferred for passivation, as some of the 400 series alloys will actually be discolored by the passivation process. Passivation imparts a limited neutral salt spray corrosion protection to the stainless steel, usually not much over 2 hours. It is critical when making assemblies that will need passivated; that all component parts be made of the same alloy; different alloys may be indistinguishable before passivation, but may have a different appearance afterward. Different passivation solutions may not only result in differences in appearance, but may result in some parts being destroyed.
Passivation of stainless steel is generally specified by QQ-P-35. It can also be specified by ASTM-380-99, ASTM-967-01 and AMS2700.