What is Stainless Steel 904L?
Stainless Steel 904L (UNS N08904 / WNR 1.4539) is a low-carbon, high-alloy austenitic stainless steel developed for use in environments containing aggressive corrosion conditions. Originally developed for resistance to dilute sulfuric acid, 904L also offers excellent resistance to other inorganic and organic acids.
Its alloying elements—especially the high levels of chromium, nickel, molybdenum, and the addition of copper—enhance its corrosion resistance beyond that of traditional 300-series stainless steels like 316L or 317L.
Chemical Composition of SS 904L
Stainless Steel 904L is a high-alloy austenitic grade with a unique composition that enhances its corrosion resistance. It contains 19.0% to 23.0% Chromium and a high Nickel content ranging from 23.0% to 28.0%, which improves resistance to reducing acids. The addition of 4.0% to 5.0% Molybdenum provides excellent protection against pitting and crevice corrosion, while 1.0% to 2.0% Copper helps resist sulfuric and phosphoric acids. It has a very low Carbon content (≤ 0.02%), making it ideal for welding applications without the risk of carbide precipitation. Manganese is limited to ≤ 2.0%, Silicon to ≤ 1.0%, and the balance is Iron, which gives it structural strength and stability.
Key Properties of Stainless Steel 904L
Corrosion Resistance
904L is highly resistant to:
- Sulfuric acid (H₂SO₄)
- Phosphoric acid
- Chloride stress corrosion cracking
- Pitting and crevice corrosion
Mechanical Strength
While not as strong as duplex or ferritic steels, 904L has excellent toughness and can be cold-worked for improved strength.
Weldability & Fabrication
Thanks to its low carbon content, 904L is easily weldable and does not require post-weld heat treatment in most cases.
Non-Magnetic Nature
SS 904L remains non-magnetic in all conditions, making it ideal for applications where magnetism must be avoided.
Applications of Stainless Steel 904L
Due to its superior resistance to aggressive environments, 904L is used in:
- Chemical Processing Equipment
- Heat Exchangers and Condensers
- Pharmaceutical and Food Processing
- Pulp and Paper Industry
- Desalination Plants
- Marine and Offshore Engineering
- Storage Tanks for Acids and Chlorides
Why Choose Stainless Steel 904L?
If your application involves high chloride concentrations, acidic solutions, or extreme temperature conditions, SS 904L offers unmatched durability. Despite its higher cost, the long-term performance and maintenance savings make it a smart investment.
Forms Available
904L Stainless Steel is available in:
- Plates & Sheets
- Pipes & Tubes
- Fittings
- Flanges
- Bars & Rods
- Wire & Electrodes
Conclusion
Stainless Steel 904L is more than just a corrosion-resistant alloy—it's a robust solution for industries that demand longevity and reliability. Whether you're designing equipment for a chemical plant or sourcing materials for offshore structures, 904L can meet the challenges where conventional stainless steels fall short.
Choose smart. Choose 904L.