904L Stainless Steel Composition & Super Austenitic Corrosion Properties

904L is a super austenitic stainless steel containing high levels of chromium, nickel, molybdenum and copper, with a carbon content limited to 0.02%. The alloy was originally developed for sulfuric acid service, and the combined addition of molybdenum and copper gives it strong resistance to reducing acids such as sulfuric and phosphoric acid, together with excellent resistance to pitting and crevice corrosion in chloride-bearing environments. Its corrosion resistance is clearly higher than that of conventional 316L.

The grade is supplied in the solution-annealed condition and does not require post-weld heat treatment, since the very low carbon content prevents carbide precipitation and intergranular corrosion in the heat-affected zone. In the annealed state it provides a minimum tensile strength of about 490 MPa, a minimum yield strength of about 220 MPa, and an elongation of at least 35%. The fully austenitic structure remains non-magnetic and stable across a wide temperature range.

904L stainless steel is supplied as plates, sheets, coils, tubes, pipes, bars and forgings, and is widely used in sulfuric acid processing plants, flue gas desulfurization systems, seawater cooling and desalination equipment, chemical reactors and storage tanks, as well as pharmaceutical and food processing equipment exposed to acidic media.