Super Stainless Steel 904L (UNS N08904)
Super Stainless Steel 904L is a high-alloy austenitic material specifically engineered for service in severely corrosive conditions. While it is classified as a stainless steel, its high nickel (25%) and molybdenum (4.5%) content often see it categorized as a "super" alloy. The defining feature of 904L is the addition of Copper (1.5%), which provides it with unparalleled resistance to strong reducing acids, most notably warm sulfuric acid.
At Aries Alloys, we supply 904L as the ultimate solution for environments where Type 316L would succumb to pitting or general corrosion. It is the premier choice for chemical processing plants and desalination facilities where aggressive chlorides and acids are part of the daily operation.
Key Performance Benefits
- Acid Specialist: Exceptional resistance to pure sulfuric acid across a wide range of concentrations and temperatures.
- Superior Pitting Defense: The high molybdenum and chromium content provides a high PREN (Pitting Resistance Equivalent Number), effectively resisting chloride-ion attack.
- SCC Resistance: Unlike standard 300-series steels, the high nickel content in 904L provides significant resistance to chloride-induced stress corrosion cracking.
- Low Carbon Integrity: The extra-low carbon content (<0.020%) ensures that the material remains immune to sensitization and intergranular corrosion after welding.
- Fully Austenitic: Remains non-magnetic in all conditions and offers excellent toughness even at cryogenic temperatures.
Technical Profile & Composition
The Copper & Nickel Synergy:
The addition of Copper is what differentiates 904L from other high-performance stainless steels. This element works in tandem with the high Nickel content to create a stable passive film that resists the aggressive "reducing" nature of sulfuric and phosphoric acids.
Mechanical & Physical Data:
- Density: 7.95 g/cm^3
- Tensile Strength: 71,000 psi (490 MPa)
- Thermal Conductivity: Good thermal transfer properties for heat exchanger service.
- Note on Welding: 904L can be welded using standard methods, but it is recommended to use over-alloyed fillers (such as 25-22-2 LMn or Alloy 625) to maintain maximum corrosion resistance in the weld metal.
Primary Industrial Use Cases
Aries Alloys is a strategic supplier of 904L for high-aggression environments:
- Chemical Processing: Equipment for the production of sulfuric, phosphoric, and acetic acids.
- Petrochemical Refineries: Gas scrubbing systems, cooling water equipment, and heat exchangers.
- Pulp & Paper: Bleaching equipment and specialized vessels for the chemical pulping process.
- Seawater & Desalination: High-pressure piping, reverse osmosis systems, and marine hardware.
- Pollution Control: Flue gas desulfurization (FGD) systems in power plants and waste incinerators.
Product Availability at Aries Alloys
We stock and supply Super Stainless Steel 904L in accordance with ASTM A240 and B625:
- Sheets & Plates: Precision-cut flat products for the fabrication of acid tanks and reaction vessels.
- Seamless & Welded Pipes: High-durability piping for chemical transport and marine cooling systems.
- Round & Hex Bars: Precision rods for machining acid-resistant valves, fasteners, and pump shafts.
- Forged Fittings: Custom flanges and elbows designed for leak-proof, high-corrosion connectivity.