A chemical treatment, usually in nitric or citric acid, that removes embedded iron and contamination left by heading, machining and handling, so a uniform chromium-rich oxide layer can form. It adds no coating and changes no dimensions, but it prevents the rust freckles that show up on untreated stainless parts. Passivated parts are verified with water immersion, humidity or copper sulfate tests.
These 18-8 screws are showing rust freckles straight out of the box, looks like somebody skipped passivation.
Also heard as
- passivate
- citric passivation
Related terms
18-8 stainless
Fastener shorthand for austenitic 300-series stainless, about 18 percent chromium and 8 percent nickel.
Galling
Adhesive wear where thread surfaces cold-weld and tear under load, seizing a nut partway down a bolt.
Zinc plating
An electroplated zinc layer, usually with a clear, blue or yellow passivate, the cheapest common fastener finish.