316L stainless steel is stainless steel, corrosion resistance is very strong, the texture is very good. The main ingredient is Fe, Cr, Ni, Mo, close to the density of iron, the general does not affect the human skin. Swiss watches are usually made of this material case, crown and strap.
904L stainless steel:
904L stainless steel is a super-heat-resistant stainless steel alloy with up to 21% chromium content, making it corrosion-resistant enough to compete with precious metal materials. Currently only used in high-tech fields, such as aerospace, chemical and petrochemical industries, but also used in surgical transplants. In 1988, Rolex took the lead in introducing 904L stainless steel into the watchmaking field, and is by far the only company in the industry that extensively and systematically applies this material to watch cases, crown and strap manufacturing.
904L stainless steel manufacturing process is quite harsh. After the first casting, the metal will be re-dissolved into a vacuum vessel, purified to remove impurities contained therein, and confirmed by scanning electron microscopy before being used in the manufacture of watches. Due to the extremely hardened stainless steel, this is a tremendous challenge to the manufacturing and stamping process - it has to be processed with special tools and processes, including rolled steel, die stamping, and finally watch parts.
316L and 904L austenitic non-magnetic steel, 904L contains nickel, chromium and copper, 316L does not have. 904 is more corrosion-resistant than 316L steel case.