Metallic and other inorganic coatings - Electropolishing as a means of smoothing and passivating stainless steel (ISO/FDIS 15730:2022); German and English version prEN ISO 15730:2022 / Note: Date of issue 2023-01-13*Intended as replacement for DIN EN I...
1Key Takeaways
This document specifies the information that the client must provide to the contractor, the requirements for electropolishing and the test methods for electropolishing for smoothing and passivating the stainless steel alloy series S2XXXX, S3XXXX and S4XXXX and precipitation hardening alloys (for information on chemical…
2Expert Interpretation
Comprehensive analysis of the technical requirements for stainless steel electropolishing as outlined in DIN EN ISO 15730:2023, including electrolyte formulation, current density control, surface quality inspection methods, and five passivation test procedures. This section covers surface finishing and passivation treatments for S2XXX-S4XXX stainless steels.
Analysis of the Standard's Core Content
DIN EN ISO 15730:2023, a key standard in the field of inorganic metal coatings, systematically regulates the electropolishing process for stainless steel. This standard applies to the surface treatment of austenitic and martensitic stainless steels in the S2XXX, S3XXX, and S4XXX series.
Technical Parameter Comparison
| Parameters | 2016 Edition | 2023 Edition |
|---|---|---|
| Electrolyte Formula | Sulfuric Acid + Phosphoric Acid Mixture | Clearly mix 96% sulfuric acid + 85% phosphoric acid by equal volumes |
| Current Density | ≥5A/dm² | Unchanged |
| Processing Time | 2-4 minutes | Newly added explanation of extended time for complex parts |
Key Process Control Points
Electrolyte Management
Appendix A of the standard recommends using a 1:1 volume ratio of 96% sulfuric acid to 85% phosphoric acid mixture. The operating temperature must be maintained at 75±2°C. The cathode material can be stainless steel, copper, or lead.
Surface Quality Requirements
The electropolished surface should be free of visible defects (scratches, pits, streaks, etc.) when visually inspected at a distance of 0.5 meters. The metal removal is typically 5-10μm, and can reach 50μm in special cases.
Passivation Test Method
- Water Immersion Test: 8 cycles (1 hour immersion + 2 hours drying)
- Humidity Test: 24 hours at 38°C/100%RH
- Neutral Salt Spray Test: ≥ 2 hours per ISO 9227
- Copper Sulfate Test: Observe for copper precipitation after a 6-minute contact time
- Potassium Ferrocyanide Test: No dark blue color should appear within 30 seconds
Implementation Recommendations
Safety Precautions
The electropolishing process generates a mixture of hydrogen and oxygen gases. An explosion-proof ventilation system must be installed. Residual electrolyte must be removed with a 10-30% nitric acid solution or graded water washing. Alkali neutralization is prohibited.
Complex Parts Processing Solution
For workpieces with complex geometries, it is recommended to:
1. Add an auxiliary cathode
2. Extend the processing time
3. Use a dedicated electrolyte (such as a low-sludge formula)