Passivation surface finish
Passivation applied by YiguProto

Surface finish

Passivation for CNC & Molded Parts

Passivation cleans and protects stainless steel. It removes free iron so the chrome layer can defend the metal.

  • Boosts stainless steel corrosion resistance.
  • Removes surface contaminants, not metal.
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What it is

What Is Passivation?

Passivation is a chemical treatment for stainless steel. The part is soaked in citric or nitric acid. This removes free iron and other contaminants from the surface. It lets the chromium in the steel form a thin, stable oxide that naturally resists rust.

Passivation does not add a coating. It strengthens the stainless steel's own protective layer.

How it works

How Passivation Works

Clean

We degrease and remove oils and shop soil.

Bath in acid

Citric or nitric acid dissolves free iron.

Rinse

Pure water rinses away the acid and loosened iron.

Dry & test

We dry the part and may run a corrosion test.

Citric acid passivation is the common, safer choice and meets ASTM A967.

Why choose it

Benefits of Passivation

Better corrosion resistance

Restores the stainless protective film.

Removes contaminants

Strips free iron that starts rust.

No dimension change

Chemistry only, no metal removed.

Clean & bright

Improves surface cleanliness.

Typical specs

Typical Passivation Specifications

SpecificationTypical range / valueNotes
MethodsCitric acid (ASTM A967), nitric acid
Material removedNone (contaminants only)
Base materialsStainless steel (300/400 series)
ColorNatural stainless tone

Best applications

When to Use Passivation

Medical devices

Surgical and instrument parts.

Food & pharma

Hygienic process equipment.

Aerospace

Corrosion-critical assemblies.

Marine parts

Components near salt water.

Materials

Compatible Materials for Passivation

We apply Passivation to the materials below. Not sure if your material qualifies? Our engineers will confirm it for free.

Stainless steel 304Stainless steel 31617-4 PH440COther stainless grades

Our solution

Our Passivation Solution

We passivate stainless steel by ASTM A967 using citric acid. It is the right step after machining to maximize corrosion resistance.

  • Citric acid process, safer and RoHS friendly.
  • Removes free iron from machining.
  • Corrosion (high-water) testing available.
  • Machining and passivation in one order.
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Passivation after machining is critical; cutting fluids and tool steel contact can leave free iron that rusts.

Design tips

Design & DFM Tips for Passivation

Passivate after machining

Do it once cutting is complete.

Avoid carbon steel contact

Mixed metals can leave iron behind.

Test if needed

Ask for a corrosion verification test.

FAQ

Passivation — Frequently Asked Questions

Send your drawings or 3D files. Most quotes come back within a few hours on business days, never more than 24 hours.
Yes. All customer files and ideas are treated as confidential. We sign NDAs when needed.
Yes. Our engineers review your design and suggest changes that cut cost, improve quality, or speed up delivery.
For Passivation, we support one-off prototypes and full production runs. There is no strict MOQ.
We can make samples for your approval. Cost depends on the process, and it is credited back on a production order.
It removes free iron so stainless steel forms its own rust-resistant film.
No. It is a surface chemistry step only.
We use citric acid per ASTM A967; it is safer and effective.
Yes, machining can leave iron that causes rust if not removed.

Need Passivation on your parts?

Send your files and get a finish recommendation + factory-direct quote.

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