STAINLESS STEEL PASSIVATION

Passivation restores the corrosion-resistant layer of the surface of stainless-steel manufactured parts.

Passivation is by definition the removal of “free iron” from the surface of a metal like stainless-steel. Although stainless steel is inherently passive, once the manufacturing process is complete, many stainless-steel parts will lose the protective chromium oxide layer, which will cause stainless-steel parts to rust or corrode.

Why stainless steel corrodes

Most stainless steel purchased for the manufacturing process has been rolled, machined and or manipulated with carbon or tempered steel instruments. This means that stainless steel purchased or re-manufactured will have a considerable amount of steel worked into the surface.

In the metal fabrication process, a surface impregnated with steel is referred to as “free iron.” When this free iron begins to react with harsh environments, salt-water, chlorine and other chemicals it will begin to corrode the stainless-steel part or component. Once started, the corrosion of the stainless steel will continue to take place, even if the presence of free iron has been removed.

Achieving stainless steel passivation through electropolishing

Electropolishing begins to enrich the surface of the stainless-steel part or component with chromium and nickel, at which point, a chemical reaction takes place during the processing of the part. The chromium reacts and forms a chromium oxide layer over the entire surface of the metal. This process is referred to as “chromium enriched surface oxidizing” and forms a passive layer which is commonly referred to in the industry as “passivation.”

Electropolishing is a popular option for many manufacturers, particularly those involved with the manufacturing of medical devices, scientific and lab equipment, marine and food service products.

The corrosion resistance through Electropolishing is compliant with ASTMB 912, ASTM A967, and ASTM A380 “Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts.”

At New England Electropolishing, we recommend electropolishing to enable the growth of a natural, inert, oxide layer on all grades of stainless steel. We also offer the nitric and citric acid immersion passivation, however, and recognize there are times when they might be preferable. We look forward to talking to you about which process is best suited for your stainless-steel products.