Stainless Steel 904L Round Bar

904L (UNS N08904) is a high-alloy austenitic stainless steel, and bar is normally ordered to ASTM A276 / A276M and ASTM A479 / A479M, with dimensions to ASTM A484 / A484M. European practice specifies it as grade 1.4539 to EN 10088-3.

The composition is low-carbon 20Cr-25Ni-4.5Mo with a deliberate 1-2% copper addition. High nickel resists stress corrosion cracking in chloride environments, molybdenum handles pitting and crevice attack, and copper is what lifts performance in sulphuric and phosphoric acid. Carbon is capped at 0.020%, so the grade resists sensitisation and can be welded in heavy sections without post-weld heat treatment.

Bar is supplied solution annealed, normally treated at about 1100-1150 C followed by a fast quench. It can be hot-finished or cold-finished by drawing, peeling, turning or grinding. Stock covers 6 mm to 300 mm either random or cut to length.

The structure is fully austenitic, so the bar is non-magnetic when annealed, cannot be hardened thermally, and gains strength only through cold work. Its PREN of roughly 34-36 sits between standard 316L and the 6% molybdenum super austenitic grades.

Where welding is required, over-alloyed nickel-base filler such as ERNiCrMo-3 is used to make up for molybdenum segregation in the weld metal.

904L costs considerably more than 316L, so it is normally chosen only where the service environment genuinely calls for it, and machined components are often preferred to heavy welded fabrication.

Common uses include sulphuric acid plant, pickling-line hardware, flue-gas desulphurisation equipment, seawater and brackish-water systems, pumps, valves, shafts and fasteners, spread across chemical processing, petrochemicals, pulp and paper, pollution control and offshore oil and gas.