Here’s a concise comparison of 904L, Oystersteel, 316L, and 304L, plus clarification about the “10 stainless steel kinds”:
STAINLESS STEEL GRADES COMPARISON
| Grade | Composition Highlights | Corrosion Resistance | Strength | Common Use | Notes |
|---|---|---|---|---|---|
| 304L | 18% Cr, 8% Ni, low C | Good | Medium | Kitchenware, piping | Low-carbon version of 304; weld-friendly |
| 316L | 16% Cr, 10% Ni, 2% Mo, low C | Better than 304L | Medium | Marine, medical instruments | Molybdenum improves salt resistance |
| 904L | 20% Cr, 25% Ni, 4.5% Mo, Cu added | Excellent | High | High-end watches (Rolex), chemicals | Very corrosion-resistant, expensive |
| Oystersteel | Proprietary Rolex alloy (based on 904L) | Top-tier | Very High | Luxury watch cases | Rolex’s marketing term for 904L steel |
🧪 TL;DR
- 304L → Common, affordable, general use.
- 316L → Marine grade, better corrosion resistance (due to molybdenum).
- 904L → Premium grade, high nickel and molybdenum, very corrosion-resistant.
- Oystersteel → Rolex-branded 904L with very high standards.
❓Is there a “10 stainless steel kinds”?
Yes, there are more than 10 types. Here’s a common categorization:
📚 Main Types of Stainless Steel (by microstructure):
- Austenitic (e.g., 304, 316, 904L) – non-magnetic, high corrosion resistance
- Ferritic (e.g., 430) – magnetic, less expensive, moderate resistance
- Martensitic (e.g., 410, 420) – hardenable, used for knives and tools
- Duplex (e.g., 2205) – mix of austenitic + ferritic, strong + corrosion-resistant
- Precipitation-Hardening (e.g., 17-4 PH) – very high strength
Each group contains several numbered types, so in total there are well over 10 stainless steel kinds.
✅ About 904L (just for comparison):
| Property | Value |
|---|---|
| Nickel | 24–25% |
| Chromium | 19–23% |
| Molybdenum | ~4.5% |
| Copper | ~1.5% |
| Carbon | ≤ 0.02% |
| Strength | High corrosion & pitting resistance |
| Typical Use | Rolex cases, acids, chlorides |
🧪 Why Rolex Uses 904L / Oystersteel?
Compared to 316L (used by most luxury brands):
- More corrosion-resistant (esp. against acids and seawater)
- Holds polish better over decades
- Harder to machine, but Rolex has in-house tech to process it
Rolex chose it to maximize longevity, shine, and resistance to extreme conditions, especially for professional models like:
- Submariner
- Sea-Dweller
- GMT-Master II