ATI 904L™ alloy (UNS N08904) is an austenitic stainless steel designed for a middle to high level of corrosion resistance. The alloy contains high levels of chromium and nickel with additions of molybdenum and copper to provide added corrosion resistance in certain media. The alloy is produced to low carbon levels for use in the welded condition as in welded vessels and other large and complex fabrications.

The high nickel (25%) and molybdenum (4.5%) contents of the ATI 904L™ alloy provide good resistance to chloride stress corrosion cracking, although not total resistance as judged by the extremely severe laboratory test, boiling magnesium chloride. The Chromium, molybdenum and nickel levels provide general and chloride pitting corrosion resistance above the level of Types 316 and 317 in many media. The copper addition provides added resistance to reducing media such as hot phosphoric acid and dilute sulfuric acid.

The N08904 alloy has been incorporated in ASTM and ASME specifications, and is widely and readily available in a variety of product forms, welding electrodes, and fittings. The ATI 904L™ alloy has performed well in a variety of service environments such as utility scrubbers, acid and fertilizer production. Representative corrosion data follow.