The passivation process returns the stainless steel or other metals back to its original specifications by removing unwanted debris and oils from the surface and then submerging the part into a passivating bath.
When a part is machined, various particles can permeate the surface of the base metal, weakening it’s resistance to corrosion and making the part more susceptible to environmental factors. Debris, dirt and other particles and residue such as free iron, grease and machining oils all affect the strength of the natural surface and can become embedded in the surface during the machining process. These often go unseen to the human eye and are often the cause of the deterioration.
As stated above, “passive” is defined as being less affected by environmental factors. The process improves and purifies the surface of the part. The restored surface acts like a protective coating to environmental factors such as air, water and other extreme environments.
It is important to note that passivation does not change the outward appearance ofthe base metal.
Passivation is used to improve the surface condition of stainless steel by dissolving the iron that is embedded in the surface by forming, machining, or other manufacturing steps.
If allowed to remain the iron corrodes and often gives the appearance of large or small rust spots on the stainless steel. In order to prevent this condition on the finished parts, they are given a passivation treatment.
This treatment, which consists of immersing the stainless steel parts in a solution of nitric acid without oxidizing salts for a specific period of time, will dissolve the embedded iron and restore the original corrosion-resistance surface by forming a thin transparent oxide film.
Passivating is used as the cleaning operation for castings, stampings and finished machine parts by immersing the parts.