Overview: 904L Stainless Steel (UNS N08904) / 1.4539
904L is a non-stabilized super-austenitic stainless steel with low carbon content. Benchmarked against ASTM B625, it features high levels of nickel and molybdenum, providing superior resistance to stress corrosion cracking and localized corrosion in aggressive environments like sulfuric acid and chloride solutions.
Specifications & Standards by Product Form
| Product Form | ASTM / ASME Standards |
|---|---|
| Round Bar | ASTM B649 / ASME SB649 |
| Seamless Tube | ASTM B677 / ASME SB677 |
| Forgings | ASTM B649 / ASME SB649 |
| Strip / Plate | ASTM B625 / ASME SB625 |
Chemical Composition (ASTM B625 / UNS N08904)
| Element | Ni | Cr | Mo | Cu | Mn | Si | C | Fe |
|---|---|---|---|---|---|---|---|---|
| Range (%) | 23.0-28.0 | 19.0-23.0 | 4.0-5.0 | 1.0-2.0 | ≤2.0 | ≤1.0 | ≤0.02 | Bal. |
Mechanical Properties (Typical at Room Temp)
| Property | Tensile Strength (MPa) | Yield Strength 0.2% (MPa) | Elongation (%) | Hardness (HBW) |
|---|---|---|---|---|
| ASTM B625 Min. | 490 (71 ksi) | 220 (31 ksi) | 35 | ≤192 |
Material Characteristics & Applications
- Superior Acid Resistance: Specifically designed for resistance to sulfuric acid at all concentrations.
- High Chloride Resistance: High nickel and molybdenum content makes it resistant to chloride stress corrosion cracking (SCC) and pitting.
- Formability & Weldability: Fully austenitic structure provides excellent toughness and ease of fabrication.
Primary Applications: Flue gas desulfurization (FGD) systems, chemical processing, pharmaceutical manufacturing, and offshore oil platforms.
Global Project Case: Flue Gas Desulfurization (FGD)
Hangbo Alloy supplied 904L plates and tubes for a thermal power plant’s FGD scrubber unit. The flue gases contained high concentrations of sulfur dioxide and chlorides, creating a highly corrosive acidic condensate. 904L was chosen to replace standard stainless steels, providing the necessary resistance to general corrosion and pitting, which extended the scrubber's maintenance cycle from 12 months to 36 months.
Pros & Cons
- Pros: Excellent resistance to sulfuric and phosphoric acids, non-magnetic, and high ductility.
- Cons: More expensive than 316L; lower strength than duplex grades like 2205.
Deep FAQ: 904L for Acidic and Marine Service
- Why choose 904L over 316L in sulfuric acid? 904L contains much higher nickel and molybdenum, plus copper, which significantly reduces the corrosion rate in sulfuric acid compared to 316L.
- Is 904L considered a "Super Austenitic" steel? Yes, because of its high alloy content and specialized corrosion resistance, it is classified as a super-austenitic grade.
- How does 904L perform in seawater? It has excellent resistance to seawater corrosion, but for stagnant seawater or high-temperature marine applications, 254SMO or Super Duplex may be required to prevent pitting.
- Is 904L magnetic after cold working? Being fully austenitic, 904L remains non-magnetic even after significant cold work.
- Can 904L be used for pharmaceutical equipment? Yes, its smooth surface finish and resistance to cleaning agents make it ideal for high-purity pharmaceutical and biotechnology applications.
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