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When I browse the official Rolex website, I always read one word—904L. Why Rolex always indicate this word and proud of it? Let’s see it.

904L is a high-alloy austenitic stainless steel with only a little carbon content. It is standardized and approved for pressure vessel use in some countries. Unlike traditional austenitic grades, 904L is not very sensitive to precipitation ferrite and sigma phases.

Because there are chromium, nickel (results in better resistance to stress corrosion), molybdenum and copper (results in resistance to sulphuric and other reducing acids) in it, 904L has good resistance to corrosion, especially in sulfuric and phosphoric and chloride condition. Both pitting and crevice attack could be prevented. Even though 904L express well in acid resistance, it is not the best one in fact. Additionally, it has a good performance in warm sea water and high chloride environments. However, 904L should not be used above about 400℃.

The 904L can also avoid magnetization in all conditions. Moreover, it is also an excellent weldability and formability alloy. 904L could be welded by all standard methods. It is high in purity, but low in sulphur grade, so it can not be machine well. Austenitic structure also gives 904L steel excellent toughness, even in cryogenic temperatures.

Appendix: 904L Chemical Composition %

C: Max 0.02;

Cr: 19.0-23.0;

Cu: 1.0-2.0;

Mn: Max 2.0;

Mo: 4.0-5.0;

Ni: 23.0-28.0;

P: Max 0.045;

S: Max 0.035;

Si: Max 1.0.