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Improve corrosion resistance and surface cleanliness of your stainless-steel parts with professional passivation service. Compliant with ASTM, AMS, and ISO standards.
Passivation is a chemical treatment that removes free iron and surface contaminants from stainless steel, restoring the metal's chromium-rich passive layer. This invisible oxide film significantly enhances corrosion resistance without altering dimensions, appearance, or mechanical properties.
We provide two types of passivation based on customer requirements and industry standards:
① Nitric Acid Passivation
Utilizes rotating cutting tools for high-precision machining of flat surfaces, curves, and complex parts, ideal for mold making, aerospace, and automotive industries.
Uses rotating workpieces and cutting tools for efficient machining of cylindrical components, widely applied in shafts, discs, and precision parts manufacturing.
Enables multi-angle precision cutting, reducing setups and machining complex surfaces, perfect for high-end aerospace, medical devices, and precision mold manufacturing.
During machining, handling, and storage, stainless-steel surfaces may be exposed to iron, carbon steel particles, cutting fluids, or environmental contaminants. These impurities weaken the natural oxide layer and may lead to:
Passivation removes these contaminants and rebuilds the protective layer, ensuring long-term stability.
Passivation forms a stable oxide layer that prevents free iron from reacting with moisture.
The chemical reaction only affects the surface and does not add or remove material.
It dissolves oils, metal particles, and carbon steel residue from machining.
The passive film offers lasting protection in humid, chemical, or salt-rich environments.
It removes microscopic contaminants to meet medical and aerospace standards.
Provides corrosion protection without needing coatings or plating.
Passivation is designed specifically for stainless steels.
Most common stainless steels used in machining; passivation enhances corrosion resistance and cleanliness.
High strength and corrosion resistance; passivation helps stabilize the protective film after machining.
Common in aerospace and medical applications; passivation improves performance in harsh environments.
Often used for knives, tools, and high-strength components; passivation removes iron residue and prevents rust.
| Material | Reason |
| Aluminum | Requires anodizing to build a protective oxide layer |
|---|---|
| Carbon steel | Does not form a passive film like stainless steel |
| Brass / Copper | Different chemical reactions that cannot form passivation |
| Titanium | Naturally forms a strong oxide film, passivation unnecessary |
These materials require different surface treatments such as anodizing, plating, or chemical conversion coatings.
Passivation uses nitric acid or citric acid to remove free iron and create a chromium-rich oxide layer. This passive layer improves corrosion resistance and restores stainless steel to its optimal condition.
| 01 |
Pre-Cleaning & Degreasing
Removing oils, fingerprints, and machining residues to ensure the
stainless-steel surface is fully prepared for chemical treatment.
Notes:
Ensures uniform reaction during passivation.
Standards:
In-house PAS-SOP-01;
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| 02 |
Contaminant & Residue Removal
Eliminating embedded iron, metal particles, and surface contaminants left
from machining or handling.
Notes:
Prevents rust caused by carbon steel contamination.
Standards:
In-house PAS-SOP-02;
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| 03 |
Acid Passivation Treatment
Immersing the parts in nitric or citric acid to dissolve free iron and
reform the chromium-rich passive layer.
Notes:
Restores optimal corrosion resistance.
Standards:
In-house PAS-SOP-03;
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| 04 |
Rinsing & Neutralization
Thorough rinsing to remove acid residues followed by neutralization to
stabilize the surface.
Notes:
Prevents acid stains and ensures safety for final use.
Standards:
In-house PAS-SOP-04;
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| 05 |
Drying
Controlled drying to eliminate moisture and avoid water spots or oxidation
marks.
Notes:
Ensures a clean, residue-free surface.
Standards:
In-house PAS-SOP-05;
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| 06 |
Corrosion Resistance Testing (Optional)
Performing salt-spray or chemical immersion tests based on customer or
industry requirements.
Notes:
Verifies durability in harsh environments.
Standards:
In-house PAS-SOP-06;
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| 07 |
Final Inspection & Packaging
Inspecting the surface quality, cleanliness, and passivation consistency
before secure packaging.
Notes:
Ensures product stability during transportation.
Standards:
In-house PAS-SOP-07;
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Typical passivation issues and how to avoid them.
Cause:Residual machining debris, embedded iron particles, or insufficient cleaning before passivation.
Impact / Prevention:
Cause:Improper rinsing, low-grade water, or contamination inside the passivation bath.
Impact / Prevention:
Cause:Excessive immersion time or overly strong acid concentration.
Impact / Prevention:
Cause:Residual acid left on the surface or uneven neutralization.
Impact / Prevention:
Ensures long-term corrosion resistance for brackets, hinges, actuators, and structural stainless parts exposed to harsh environments.
Provides ultra-clean, contamination-free surfaces ideal for surgical tools, implants, and stainless housings.
Protects shafts, fittings, housings, and fasteners used in automated machinery from rust and chemical degradation.
Improves durability of exhaust components, connectors, decorative metal trims, and high-wear stainless parts.
Typical passivation parameters for stainless-steel CNC machined parts.
| Parameter | Typical Range | Description |
| Acid Type | Nitric / Citric | Defines corrosion resistance level and surface cleanliness |
|---|---|---|
| Acid Concentration | 4% – 25% (based on type) | Higher concentration improves oxide formation efficiency |
| Temperature | 20°C – 60°C | Higher temperature accelerates chemical reaction |
| Immersion Time | 10 – 30 minutes | Ensures complete removal of free iron and contaminants |
| Rinse Cycles | 2–3 cycles | Removes residual acids to prevent staining or etching |
| Neutralization | Optional (alkaline bath) | Used for sensitive parts or strict cleanliness requirements |
| Final Film Thickness | 1–5 nm | Ultra-thin passive film with no dimensional change |
| Surface Condition Requirements | Free from oils & residues | Clean surface ensures even and effective passivation |
Citric passivation is preferred for medical and aerospace parts requiring high
cleanliness.
Nitric passivation is suitable for higher corrosion resistance or industrial-grade parts.
Send us your part files or design drawings. Our surface finishing experts will evaluate the part geometry, surface requirements, and production volume and recommend the ideal machining process for your CNC machined parts.
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