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Passivation

Passivation: Enhancing Corrosion Resistance for Stainless Steel and Alloys
  • Superior Corrosion Resistance
  • Contaminant Removal
  • Preserves Aesthetics
  • Medical & Aerospace Approved
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Passivation Surface Finish

What's Passivation

Passivation is a chemical treatment process that removes free iron and other surface contaminants from stainless steel and other alloys, while simultaneously promoting the formation of a thin, transparent, and protective chromium oxide layer. This enhanced passive layer significantly improves the material’s inherent corrosion resistance without altering its appearance or dimensions. It is critical for applications where cleanliness, corrosion prevention, and material integrity are paramount, especially in medical, aerospace, and food processing industries.
ParameterDescription
Applicable MaterialsPrimarily stainless steels (all grades). Also applicable to titanium, cobalt-chrome, and some other alloys.
ColorNo change to the base material color. The passive layer is transparent.
Surface Roughness (Ra)Does not significantly alter the base material’s surface roughness. The process is non-etching and non-abrasive.
Visual AppearanceMaintains the original metallic luster and finish of the part. No visible coating or color change.

Types of Passivation Surface Finishes

★The traditional and most widely used passivation process.
Process: Parts are immersed in a nitric acid bath (typically 20–50% concentration) at controlled temperatures.

Nitric Acid Passivation

★A safer, environmentally friendly alternative to nitric acid passivation.
Process: Uses citric acid solutions to chelate iron contaminants rather than dissolve them aggressively.

Citric Acid Passivation

★Overview: Combines chemical and electrical treatment to accelerate oxide layer formation.
Process: The metal part acts as an anode in an electrolyte solution; an electric current promotes oxidation.

Electrochemical Passivation

Advantages of Passivation

Superior Corrosion Resistance

Maximize the inherent corrosion resistance of stainless steel by removing surface contaminants and promoting the formation of a robust, passive oxide layer.

No Dimensional Change

The process removes microscopic amounts of free iron from the surface without altering the dimensions or weight of the part, making it ideal for precision components.

Preserves Aesthetic Appearance

Passivation does not change the color, luster, or visual appearance of the metal.

Removes Contaminants

The process effectively cleans the surface of any free iron, dirt, or other foreign materials introduced during machining or handling.

Improved Cleanliness

A passivated surface is cleaner and less reactive, which is critical for medical, pharmaceutical, and food-grade applications.

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Limitations to Notice

  • Does Not Remove Discoloration: Passivation will not remove heat tint or discoloration from welding or heat treating. These must be removed mechanically or chemically prior to passivation.
  • Limited to Specific Materials: Primarily effective on stainless steels and certain other corrosion-resistant alloys. It is not a rust-proofing treatment for carbon or low-alloy steels.

Design Considerations

Material Selection

Ensure that the grade of stainless steel is appropriate for the intended environment and that it can be effectively passivated.

Welding and Heat Treating

If parts are welded or heat-treated, they must be properly cleaned to remove any scale or heat tint before passivation. Mechanical grinding or acid pickling may be required.

Crevices and Blind Holes

Ensure that the design allows for proper cleaning and rinsing of all surfaces, including tight crevices and blind holes, to prevent trapping of cleaning or passivation solutions.

Specify the Standard

Clearly specify the required passivation standard (e.g., ASTM A967) and any specific test methods required for verification.

Passivation Processed Parts

Passivation Processed Part 1
Passivation Processed Part 5
Passivation Processed Part 4
Passivation Processed Part 2
Passivation Processed Part 3
Passivation Processed Part 6

FAQs

Passivation is primarily used for various grades of stainless steel. It can also be applied to other alloys like titanium and cobalt-chrome to enhance their corrosion resistance.
Passivation can remove free iron from the surface of stainless steel, allowing its inherent chromium to form a protective, corrosion-resistant oxide layer. It's crucial for maximizing stainless steel's corrosion resistance, especially after manufacturing processes that can embed free iron.
No, passivation does not alter the aesthetic appearance, color, or dimensions of the part. The protective oxide layer formed is transparent and extremely thin, making it ideal for precision components.
Both nitric and citric acid passivation effectively remove free iron and promote the passive layer. Citric acid is generally considered a more environmentally friendly and safer alternative, often preferred for medical and food-grade applications, while nitric acid is a traditional and highly effective method.

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