Stainless steel is widely used in the industry due to its high corrosion resistance and aesthetic appearance. However, after manufacturing processes, surface oxides, machining residues, burrs, and contaminants can negatively impact the material’s performance. Therefore, surface treatment methods such as electropolishing and passivation are applied to process and protect stainless steel surfaces.
What is Stainless Steel Surface Treatment?
Stainless steel surface treatment is a general term for processes that improve, clean, and protect the surface using mechanical, chemical, or electrochemical methods. Proper surface treatment enhances the aesthetic appearance of the steel while increasing its corrosion resistance, thereby extending its lifespan.
What is Electropolishing?
Electropolishing is an electrochemical surface treatment method that removes microscopic roughness, polishes, and cleans the stainless steel surface.
Electropolishing Process Steps
✔ Pre-Cleaning: Oils, oxides, and dirt on the surface are removed.
✔ Electrolytic Bath: The part is placed in a bath, typically containing phosphoric acid (H₃PO₄) and sulfuric acid (H₂SO₄).
✔ Application of Electrical Current: The part acts as the anode, while another metal in the electrolyte acts as the cathode.
✔ Microscopic Level Etching: Surface irregularities dissolve, smoothing the material’s surface.
✔ Rinsing and Drying: Acid residues are completely removed.
What is Passivation?
Passivation is a chemical surface treatment that enhances the protective oxide layer on stainless steel. It removes free iron particles from the surface, allowing the material to regenerate its natural chromium oxide layer.
Passivation Process Steps
✔ Pre-Cleaning: Oils, dirt, and metal residues are removed.
✔ Chemical Bath: Stainless steel parts are immersed in a solution containing nitric acid (HNO₃) or citric acid (C₆H₈O₇).
✔ Waiting Period: The steel surface is left for a specified time to form a natural chromium oxide layer.
✔ Rinsing and Drying: Acid residues are removed, and the part is ready for use.
Differences Between Electropolishing and Passivation
| Feature | Electropolishing | Passivation |
|---|---|---|
| Process Method | Electrochemical | Chemical |
| Surface Brightness | ✔ Provides mirror-like shine | ❌ Does not enhance brightness |
| Microscopic Roughness Removal | ✔ Yes | ❌ No |
| Corrosion Resistance | ✔ Very high | ✔ High |
| Free Iron Removal | ✔ Yes | ✔ Yes |
| Hygienic Surface | ✔ Ideal for medical and food industries | ✔ Suitable for chemical and industrial use |
| Application Area | Decorative and precision surface finishing | Industrial protection and maintenance |
Conclusion: Which Method Should Be Preferred?
• If the stainless steel surface needs to be both bright and ultra-smooth, electropolishing is recommended.
• If the goal is simply to enhance the corrosion resistance of stainless steel, passivation will be sufficient.
• Electropolishing is preferred in medical, food, and pharmaceutical applications, while passivation is sufficient for chemical and industrial applications.
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