904L steel watch case

904L steel is a high-grade stainless steel alloy commonly used in watchmaking, especially for watch cases. It is highly corrosion-resistant and often preferred over standard stainless steel alloys.

One of its biggest advantages is resistance to sweat, seawater, and harsh environments. It is also very durable and maintains its finish over long-term use.

Rolex is one of the most famous brands using 904L steel. They note it is harder to machine, but offers a brighter finish and stronger corrosion resistance.

Overall, 904L steel is considered a premium material in watchmaking, combining durability, corrosion resistance, and aesthetic appeal.

What is the ratio of TC4 titanium alloy to 316L stainless steel to 904L stainless steel in terms of durability and resistance to impact?

This is mainly a comparison of strength and hardness. In annealed condition, TC4 titanium has much higher tensile strength (~900 MPa) and hardness (~35 HRC). 316L and 904L stainless steel are around 480–490 MPa with ~90 HRB hardness.

316L and 904L are mainly designed for corrosion resistance and processing ease, not extreme strength. TC4 titanium is designed for high strength and better impact resistance.

From a pure material performance perspective, TC4 is stronger. If stainless steel is required, martensitic stainless steel (like 420) offers higher hardness. Composite structures such as carbon fiber + titanium shell can provide even better performance.

Why do only Rolex use 904L stainless steel while other brands mostly use 316L?

The difference in cost is actually very small, since each watch only uses about 100g of steel.

In real-world use, 316L already provides excellent corrosion resistance in most environments, including sweat, air, and seawater exposure.

904L has slightly better resistance in extreme chemical conditions, but such conditions are rare in daily watch use.

Therefore, the use of 904L is often more about branding and positioning than a significant functional improvement.