From 2B to 8K: How to Achieve a No.8 Mirror Finish on Stainless Steel
Introduction
This guide explains how to transform stainless steel from a 2B starting surface to a true 8K (No.8) mirror finish. You’ll learn the full production sequence—from cleaning and grinding to polishing, drying, protective film application, and packing. Whether you’re an architect, fabricator, or procurement manager, this article will help you understand both the process and the choices involved.
What Do 2B, BA, No.4, Hairline, and 8K/No.8 Actually Mean?
- 2B Finish: Cold-rolled, annealed, and skin-passed. Smooth, matte, and economical. The most common starting point for mirror polishing.
- BA (Bright Annealed) Finish: Bright, reflective surface from annealing in a controlled atmosphere. Can reduce 1–2 grinding steps if used as starting material.
- No.4 Finish: Brushed finish with uniform short parallel lines.
- Hairline Finish: Long, continuous brushing pattern with decorative effect.
- 8K / No.8 Mirror Finish: A true mirror-grade finish with high reflectivity and minimal surface roughness.
👉 Note: “8K” and “No.8” describe the same mirror-grade finish.
Start Right: Substrate Matters
- From 2B: Standard practice in most polishing lines. Requires full pre-grinding sequence.
- From BA: Can save time and steps, suitable for premium projects.
In most cases, 2B finish is the standard starting point for 8K polishing.
Step-by-Step: From 2B to 8K
Our production lines can polish both coil and sheet in a continuous process. A complete production run includes:
- Cleaning – Remove oil, dust, and residues.
- Pre-grinding – 320 → 400 → 600 grit (eliminates 2B texture).
- Fine Grinding – 800 → 1000 → 1200/1500 → 2000 grit.
- Polishing – Sisal → cotton → flannel wheels with Al₂O₃ or Cr₂O₃ compounds.
- Final Cleaning – Remove polishing paste residues.
- Drying – Ensure a spotless surface.
- Protective Film Application – Standard or laser-safe film.
- Packing – Prepared for shipment.
Quality Targets & Inspection
- Surface Roughness (Ra): Mirror surfaces typically target Ra ≤ 0.05 μm.
- Visual Standards: No orange peel, drag marks, pits, or black shadows.
- Protection: High-adhesion protective film prevents scratches during handling and transport.
Material Choices: 430 vs 201 vs 304 vs 316L
We polish the following grades to 8K mirror finish:
- 430: Cost-effective, achieves mirror finish, but with lower corrosion resistance.
- 201: Economical, bright surface, less corrosion resistance.
- 304: Standard grade, stable mirror finish, widely used in various industries.
- 316L: Premium grade, superior corrosion resistance, ideal for coastal or outdoor environments.
Common Defects & Troubleshooting
- Orange Peel: Insufficient pre-grinding or uneven base → Re-grind evenly.
- Pitting / Black Shadows: Contamination or worn polishing compound → Clean and replace consumables.
- Drag Marks: Skipping grit sizes → Follow complete grit sequence.
- Overheating & Warping: Excessive pressure or poor cooling → Reduce pressure, improve cooling.
Applications & Design Notes
8K mirror stainless steel is widely used in:
- Elevator doors and cabins
- Architectural facades and cladding
- Interior decorative panels and screens
- Doors, signage, and luxury furniture
Design Tips:
- Use protective film (standard or laser film) until installation.
- Account for corner radii and joint alignment to avoid distortion.
- Apply anti-fingerprint coatings for high-touch applications.
Cost & Lead Time Drivers
Key factors influencing cost and delivery:
- Grade selection (430, 201, 304, 316L)
- Thickness and size (coil or sheet)
- Starting surface (2B vs BA)
- Production yield and defect control
- Level of automation in production line
Frequently Asked Questions (FAQ)
Q: What’s the difference between 8K and No.8 mirror finish?
A: They describe the same mirror-grade finish. “8K” is common in Asia, while “No.8” is used in ASTM standards.
Q: Which stainless grades can be polished to 8K?
A: 430, 201, 304, and 316L are all suitable for 8K polishing.
Q: Can both coils and sheets be polished?
A: Yes. Our lines are capable of handling both forms continuously.
Q: Why is 2B the common starting point?
A: Most production lines are optimized for 2B, though BA can reduce polishing steps.
Q: What Ra value is considered mirror finish?
A: Ra ≤ 0.05 μm is typically specified.
Conclusion & Call to Action
Producing 8K mirror stainless steel involves cleaning, multi-stage grinding, polishing, drying, protective film application, and packing—all completed on one production line. With the right substrate and controlled process, the result is a flawless mirror finish suitable for elevators, facades, doors, and interiors.
Need mirror-grade samples or a quick quote? We supply 430, 201, 304, and 316L in 8K mirror finish—available in coils or sheets. Contact us today for a same-day quotation and sample dispatch.
