Passivation for Stainless and Titanium Parts
Nitric and citric passivation per ASTM A967 for 303, 304, 316L, 17-4PH and titanium parts, with free-iron removal verified and certificates in the shipment.
Passivation at KGL
Passivation is a chemical bath, not a coating: acid removes free iron from the stainless surface and lets the chromium oxide layer rebuild, so the part resists corrosion as designed. KGL runs passivation through an audited partner line per ASTM A967, nitric or citric per the drawing, with incoming cleaning and post-process verification handled in house.
When to Choose It
| Part and alloy | Route | Why |
|---|---|---|
| 303, 304, 316L machined fittings and fluid parts | ASTM A967 nitric or citric | corrosion service, marine, medical adjacent |
| 17-4PH valve and instrument parts | ASTM A967 per condition | H900 and aged conditions |
| Medical instruments and device components | Citric route, ISO 13485 system | cleanliness documentation |
| Titanium parts per drawing callout | ASTM F86 language | implants and surgical tools |
Specifications We Control
| Item | Specification |
|---|---|
| Standard | ASTM A967 (nitric 1 to 4, citric), ASTM F967 practice per drawing; F86 for titanium |
| Dimension change | No measurable layer; verification after process on critical faces |
| Verification | Water immersion or high humidity test per A967 practice, free iron check |
| Certificate | Passivation certificate with bath, time, temperature; RoHS/REACH available |
| Lead time | 1 to 2 working days in the normal route |
How We Run It and Check It
Route we control: degrease and clean, passivate, rinse, dry, verify, pack. The A967 verification practice (water immersion or high humidity) is run per batch on witness parts. For medical parts under our ISO 13485 system, cleaning validation notes travel with the certificate. Parts that were polished or electropolished are passivated after polishing unless the drawing says otherwise.
Material side: stainless steel CNC machining, titanium CNC machining. Related finish: polishing and electropolishing.
Cross entrances: by material | CNC machining | inspection and QC.
Frequently Asked Questions
Why does machined stainless still rust before passivation?
Free iron smears onto the surface from tooling and fixtures during cutting. It is stainless underneath, but the smeared iron rusts first. Passivation dissolves that free iron in acid without attacking the base metal, so the surface behaves like stainless again.
Nitric or citric acid, which one?
Nitric acid per ASTM A967 is the traditional route and the default on many aerospace drawings; citric routes are preferred where environmental handling or medical cleanliness matters. We follow the drawing, and where the drawing is silent we propose a route in the quote.
Does passivation change dimensions?
No measurable layer grows and only microns of surface iron are removed. Dimensions are still verified after passivation on sealing and bearing faces, and the certificate states the method used.
Do you passivate titanium too?
Yes, for medical-adjacent parts we coordinate titanium surface conditioning per drawing, commonly ASTM F86 passivation language on implants and instruments. Stainless 303, 304, 316L and 17-4PH are the everyday passivation loads.
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Quote with engineering feedback within 24 hours; prototypes in 7 to 15 days.
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