Stainless Steel Passivation
Passivation of stainless fasteners per ASTM A967 / AMS 2700 — a nitric or citric acid treatment that strips free iron so the natural chromium oxide layer forms properly, with no visible change and no added layer.
Last updated: 2026-11
Specifications
Passivation is not a coating — it is a chemical treatment (typically a nitric or citric acid bath) that removes the free iron and machining contamination left on stainless steel surfaces so the chromium oxide layer that gives stainless its corrosion resistance can form properly across the whole surface. Without it, machined stainless fasteners can show localized rust spots where embedded free iron corrodes even though the bulk material is stainless. The treatment is standard practice on stainless fasteners for aerospace and defense work and is often called out as a required process step even when the print does not spell out every detail. Two cautions matter to buyers: passivation leaves the surface clean but with reduced natural lubricity, so stainless threads can be more vulnerable to galling unless a lubricant or dry film lube is applied afterward; and it does nothing for carbon steel, which needs a sacrificial coating instead.
| Process | Chemical treatment in a nitric or citric acid bath — removes free iron and surface contaminants so the natural chromium oxide layer forms uniformly |
|---|---|
| Reference standards | ASTM A967/A967M (chemical passivation treatments, e.g. Method 2); AMS 2700 (aerospace processing); ASTM A380/A380M (cleaning and passivation practice for stainless steel) |
| Substrate | Stainless (CRES) fasteners and parts — not a coating and no layer is added; does not help carbon steel |
| Appearance | Improves corrosion resistance with little or no visual change; does not brighten or smooth the way electropolishing does |
| Corrosion resistance | Restores and enhances the natural corrosion resistance of stainless; prevents localized rust from embedded free iron on machined surfaces |
| Lubricity / galling | Clean, chemically stable surface with reduced natural lubricity — stainless threads may gall without subsequent lubrication or dry film lube (applied after passivation; pre-passivation lubrication interferes with the treatment) |
| Certification | For CRES fasteners, passivation per AMS 2700 is expected as part of the certification package unless explicitly waived |
Materials
- Austenitic stainless fasteners (304/316 class)
- Stainless aerospace and defense hardware (CRES)
- Stainless marine and food-equipment components
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (Stainless Steel Passivation) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is per batch, carried with the fastener order. Finishing run adds 5–10 days to the fastener lead time. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
Why do passivated stainless threads gall, and what prevents it?
Passivation removes the surface films and free iron that were marginally separating the mating faces, leaving clean, chemically stable metal with reduced natural lubricity. Under thread engagement pressure, austenitic stainless is prone to adhesive wear — clean metal-to-metal contact can seize. Prevention is layered: apply lubrication or a dry film lubricant after passivation (never before — pre-passivation lubrication contaminates the treatment chemistry), prefer looser thread classes where the design allows, and control handling so films or particulates do not accumulate on the passivated surface.
Does passivation change dimensions or appearance?
The passive film is thin and invisible, so passivation improves corrosion resistance without a major visual change and without the build-up a coating adds — one reason it suits threaded hardware. It is also not a polishing operation: it does not smooth the surface or remove tool marks, and where a brighter, smoother, more cleanable surface is required, electropolishing (often paired with passivation) is the complementary process.
What is the MOQ and lead time for this finish?
Finishing runs per batch carried with the fastener order and adds 5–10 days to the fastener lead time. Coated parts follow the finish line that processes them, so confirm the exact schedule against quantity and finish class at quotation.
What should an RFQ for this finish state?
State the base fastener (grade, diameter, length), the coating standard and class (or the process plus thickness/color requirement where no standard callout exists), any salt-spray or friction requirement, and quantity per size — plus destination country and required documents such as a mill test certificate.
Related knowledge
- Reading a Fastener Coating Callout: ISO 10683 Designations, Salt-Spray Hours and What to Confirm With the Plater
- Zinc-Plated vs Hot-Dip Galvanized Fasteners: Which Coating for Which Environment
- Zinc-Flake Coating for Fasteners: When the Evidence Supports It, and What to Verify at the Coater
- Zinc-Flake vs Zinc-Nickel for High-Strength Fasteners: What the Evidence Settles on Hydrogen, Salt Spray, Friction and Specs
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support