904L stainless steel is a non-stabilized austenitic stainless steel with low carbon content. This high alloy stainless steel is added with copper to improve its resistance to strong reducing acids, such as sulphuric acid.

The steel is also resistant to stress corrosion cracking and crevice corrosion. 904L is non-magnetic, and offers excellent formability, toughness and weldability. 904L contains high amounts of expensive ingredients, such as molybdenum and nickel. Today, most of the applications that employ grade 904L are replaced by low-cost duplex stainless steel 2205.