What makes stainless stainless
Passivation removes the free iron and contaminants introduced during machining, forming, and handling, then lets the chromium-rich passive oxide layer regenerate. That passive layer is the corrosion resistance — passivation restores and maximizes it.
Why machined stainless needs it
Cutting tools, fixtures, and abrasives deposit free iron on the surface. Invisible to the eye, it can cause rust spots and premature corrosion even on a high-grade alloy — sometimes called "tea staining." Passivation dissolves those deposits in an acid bath and lets the alloy re-form its protective film. The result: a stainless surface performing as its alloy intends.
- Removes free iron and metallic contamination from machining
- Restores and maximizes the chromium-oxide passive layer
- Eliminates surface rust risk on freshly machined parts
- Required or recommended by many aerospace, medical, and food specs
- No dimensional change — purely a surface chemistry treatment
Nitric vs. citric
Nitric acid is the traditional process specified by many legacy aerospace and defense standards. Citric acid is the environmentally preferred alternative, equally effective and approved by current ASTM A967 and AMS 2700 revisions. Your drawing call-out drives the choice. Passivation is the natural companion to our stainless steel machining.