Passivation Technical Information

Passivation of stainless steel alloys is the process of removing iron and iron compounds from the surface of the metal. These contaminates are often introduced through manufacturing operations such as machining, grinding and stamping. Contamination can also occur from improper handling and storage. Sulfur, which is added to some alloys for increased machineability, can also create problems. These contaminants are usually invisible to the naked eye and, if left untreated, can increase the chances of corrosion of the stainless steel.

Passivation of stainless steel to remove these contaminants can be accomplished chemically using formulations of nitric acid or citric acid. These formulations have been developed to achieve the removal of contaminants from the various stainless steel alloys (300 series, 400 series, P.H. Alloys, etc.), while at the same time avoiding any removal of the stock alloy.

It should be noted that passivation does not remove heat staining due to grinding, welding or heat treating. Heat stains and certain other types of soils should be removed by acid cleaning (pickling) the stainless steel prior to the passivation process.