FAQ’s on Stainless Steel 904L

904L is an austenitic stainless steel. In comparison to 316L, its molybdenum addition gives it superior resistance to localized attack (pitting and crevice corrosion) by chlorides and greater resistance reducing acids and in particular its copper addition gives it useful corrosion resistance to all concentrations of sulphuric acid. Its high alloying content also gives it greater resistance to chloride stress corrosion cracking, but it is still susceptible. Its low carbon content makes it resistant to sensitization by welding and which prevents intergranular corrosion.

Both of 904L and 316L are Austenite steel which are nonmagnetic and has high corrosion resistant properties, and good machining and polishing performance. As we all know, they can be be regard as substitutes for each other in some cases. The main advantage of 904L over 316L is its resistance to acids. "The addition of copper to this grade gives it greatly improved resistance to strong reducing acids, particularly sulphuric acid".

904L steel is more expensive and much more complicated to machine because of it's hardness. Rolex had to replace most of their steel production line and tools to be able to handle the change. It helps that they make all their parts in-house, most other brands have to get cases made by outside suppliers.

904L steels are commonly used in high-technology and in the aerospace and chemical industries. Their excellent anti-corrosion properties are comparable to those of precious metals.

This high alloy stainless steel is added with copper to improve its resistance to strong reducing acids, such as sulphuric acid. The steel is also resistant to stress corrosion cracking and crevice corrosion. Grade 904L is non-magnetic, and offers excellent formability, toughness and weldability.

Rolex calls 904L stainless steel a “corrosion-resistant superalloy.” 904L differs from 316L because of extra Chromium, Molybdenum, Nickel, and Copper which gives it improved resistance to acids. 316L is considered a tougher, harder, “marine grade” steel, but it does not have luster and acid resistance of 904L.