904L stainless steel is a super austenitic, low-carbon stainless steel known for its high resistance to corrosion, strength, and toughness. The material boasts high strength, alongside high corrosion and acid resistance. Due to this, it is an ideal choice in industries such as chemical processing equipment, marine and seawater cooling equipment and pharmaceutical production equipment.
High Corrosion / Acid resistance
904L stainless steel offers excellent corrosion resistance, particularly in acidic conditions. This is due to the high levels of chromium (20%), nickel (25%), molybdenum (4%) and copper (1.5%), these combined create a steel that maintains its strength in aggressive acidic environments, making 904L a better choice than other grades like 316 stainless for applications that require resistance to harsh conditions, such as sulphuric and phosphoric environments.
904L is also resistant to chloride stress corrosion cracking. The higher nickel and molybdenum content make this a superior option than standard 304/316 steels, 904L is less likely to crack under tensile strength when exposed to chloride ions. While not completely immune, the high alloying of 904L makes it a much more reliable material than low-alloyed steels.
High strength
Expanding on the above point, 904L also boasts a high tensile strength. This typically ranges between 490 and 700 MPa, further supporting its corrosion resistance in acidic or chloride rich environments.
- Tensile strength (typically 490 to 700 MPa minimum)
- Yield strength (typically 220 MPa minimum)
Low carbon content
In terms of carbon content, 904L stainless possesses an extremely low maximum content of 0.02%. This allows the material to have elevated resistance to corrosion, chromium carbide precipitation is prevented during welding which means that the material can stay stable, resisting intergranular corrosion. This reduces the need for post-heat weld treatment.
The material also offers excellent weldability. As previously mentioned, it requires no pre/post-treatment – due to its high nickel and molybdenum content. However, 904L is fully austenitic which can make it susceptible to hot cracking.
Pitting and crevice corrosion resistance
The material is engineered for exceptional resistance to pitting and crevice corrosion, particularly in harsh chloride and acidic environments. The high molybdenum/copper/nickel content means that the material can have a Pitting Resistance Equivalent Number (PREN) of roughly 34 to 43, making it a far superior choice to 316L in terms of performance.
Common applications
- Chemical processing equipment (e.g., tanks, flanges, heat exchangers, and pipes)
- Marine and seawater cooling equipment
- Desalination plants
- Gas washing plants
- Oil and gas industry components
- Pharmaceutical production equipment
