904L is a low-carbon, high-alloy austenitic stainless steel containing elevated levels of nickel and molybdenum together with copper. This carefully balanced composition provides substantially improved corrosion resistance compared with conventional 300-series stainless steels.

The copper addition provides particularly good resistance to reducing acids such as sulfuric acid, while molybdenum enhances resistance to pitting and crevice corrosion. High nickel content helps maintain a stable austenitic structure and improves resistance to stress-corrosion cracking.

The low carbon content minimizes carbide precipitation during welding and helps maintain corrosion resistance in welded structures. This makes 904L suitable for fabricated process equipment where both corrosion performance and weldability are important.

904L is widely used in chemical-processing plants, sulfuric acid systems, heat exchangers, process piping, pharmaceutical equipment, fertilizer production and pollution-control systems.