SAE 904L grade stainless steel is a fully austenic low-carbon variety of stainless steel with additives of molybdenum and copper. Its high nickel and chromium content make it corrosion resistant in both oxidizing and reducing environments. The copper and molybdenum help to make it resistant to pitting as well as crevice corrosion. The nickel content makes it resistant to chloride SCC and the low proportion of carbon makes it resistant to intergranular corrosion. It is considered especially well-suited to handling sulfuric acid and phosphoric acid, though at high temperatures it may be subject to stress corrosion cracking.
It has applications in piping systems, pollution control equipment, heat exchanges, and bleaching systems.
In 1985 Rolex became the first wristwatch manufacturer to utilize 904L grade steel in its watches. Rolex chose to use this variety of steel because it takes a higher polish than other grades of steel and provides greater corrosion resistance, though it does not machine as well and requires specialized equipment to be properly modified into the required shapes.