Product Description
904L (UNS N08904 / 1.4539) is a high-performance super austenitic stainless steel with exceptional corrosion resistance properties. This premium grade features high levels of chromium (20%), nickel (25%), molybdenum (4.3%), and copper (1.5%) to provide outstanding resistance to a wide range of corrosive environments, particularly in sulfuric and phosphoric acids.
As a multipurpose austenitic stainless steel with a Pitting Resistance Equivalent Number (PREN) of ≥34, 904L offers superior corrosion resistance compared to standard austenitic grades like 316L. The combined addition of high nickel and molybdenum content provides enhanced resistance to stress corrosion cracking, while its low carbon content (≤0.020%) ensures excellent intergranular corrosion resistance in the welded condition.
904L stainless steel is particularly valued in applications dealing with medium to severe corrosive solutions, where its balanced combination of mechanical properties and corrosion resistance makes it an ideal choice for demanding industrial environments. This versatile grade provides approximately twice the strength of conventional 300-series stainless steels while maintaining excellent ductility and impact strength.
Applications
904L super austenitic stainless steel is specifically designed for applications involving highly corrosive environments where standard austenitic grades would experience premature failure. Its exceptional resistance to acid environments and chloride-induced corrosion makes it particularly suitable for:
- Phosphoric acid production and processing equipment
- Fertilizer manufacturing facilities
- Sulfuric acid solutions and hydrometallurgy equipment
- Saline solution handling systems
- Seawater applications (with some restrictions)
- Sour gas applications (separators and processing equipment)
- Chemical processing plants with medium to severe conditions
- Tall oil distillation columns
- Pollution control equipment and flue gas desulfurization scrubbers
- Food processing equipment exposed to acidic environments
- Offshore oil and gas production equipment
- Heat exchangers handling aggressive media
The high molybdenum and copper content of 904L make it particularly effective in sulfuric acid applications, where its performance exceeds that of most other high corrosion-resistant grades. It is also widely used in the phosphoric acid industry, where its excellent corrosion resistance is maintained even in the presence of impurities like chlorides and fluorides.
Standards
904L stainless steel conforms to the following international standards:
European Standards:
- EN 1.4539 (X1NiCrMoCu25-20-5)
- EN 10088-2 (Flat Products)
- EN 10088-3 (Semi-finished products, bars, rods, wire, sections and bright products)
- EN 10216-5 (Seamless tubes)
- EN 10217-7 (Welded tubes)
American Standards:
- UNS N08904
- ASTM B625 (Plate, Sheet, and Strip)
- ASTM B673 (Welded Pipe)
- ASTM B674 (Welded Tube)
- ASTM B677 (Seamless Pipe and Tube)
- ASTM B649 (Bar and Wire)
- ASME SB625, SB673, SB674, SB677, SB649
- ASME Boiler and Pressure Vessel Code Section VIII
Grade Designations and Chemical Composition
Grade Equivalents
| UNS | EN | Common Name |
|---|---|---|
| N08904 | 1.4539 (X1NiCrMoCu25-20-5) | 904L |
Chemical Composition (weight %)
| Element | Min % | Max % | Typical % |
|---|---|---|---|
| Carbon (C) | – | 0.020 | 0.015 |
| Chromium (Cr) | 19.5 | 20.5 | 20.0 |
| Nickel (Ni) | 23.0 | 28.0 | 25.0 |
| Molybdenum (Mo) | 4.0 | 5.0 | 4.3 |
| Copper (Cu) | 1.0 | 2.0 | 1.5 |
| Manganese (Mn) | – | 2.0 | 1.0 |
| Silicon (Si) | – | 1.0 | 0.5 |
| Phosphorus (P) | – | 0.045 | 0.03 |
| Sulfur (S) | – | 0.035 | 0.003 |
| Iron (Fe) | Balance | Balance | Balance |
PREN = %Cr + 3.3×%Mo + 16×%N ≥ 34
Mechanical Properties
904L (UNS N08904 / 1.4539) super austenitic stainless steel offers an excellent combination of strength, ductility, and toughness. Its mechanical properties make it suitable for demanding applications where both structural integrity and corrosion resistance are required.
Tensile Properties
| Property | Temperature | Value (MPa) | Value (ksi) |
|---|---|---|---|
| 0.2% Yield Strength (Rp0.2) | 20°C (68°F) | 313 | 45 |
| 100°C (212°F) | 205 | 30 | |
| 300°C (572°F) | 145 | 21 | |
| 500°C (932°F) | 125 | 18 | |
| Tensile Strength (Rm) | 20°C (68°F) | 520 | 75 |
| 100°C (212°F) | 520 | 75 | |
| 300°C (572°F) | 490 | 71 | |
| 500°C (932°F) | 410 | 59 | |
| Elongation (minimum) | All temperatures | 40% | |
| Hardness | – | 180-220 HV10 | |
Impact Properties
904L exhibits excellent toughness even at cryogenic temperatures:
- Charpy V-notch: > 100 J/cm² (70 ft-lbs) at -196°C (-320°F)
Physical Properties
| Property | Value |
|---|---|
| Density | 8.05 kg/dm³ (0.29 lb/in³) |
| Modulus of Elasticity at 20°C (68°F) | 190 GPa (27.5 × 10⁶ psi) |
| Thermal Expansion Coefficient (20-100°C) | 15 × 10⁻⁶ K⁻¹ |
| Thermal Conductivity at 20°C (68°F) | 17 W·m⁻¹·K⁻¹ |
| Specific Heat at 20°C (68°F) | 500 J·kg⁻¹·K⁻¹ |
| Electrical Resistivity at 20°C (68°F) | 80 μΩ·cm |
| Magnetisable | No (except when cold worked) |
Heat Treatment
904L stainless steel should be solution annealed (solution treated) between 1095°C and 1150°C (2000°F and 2100°F) followed by rapid cooling, typically water quenching. This treatment ensures optimal corrosion resistance by dissolving any carbides or intermetallic phases that might have formed during processing, and retaining the elements in solid solution.
Available Dimensions
FUSHUN METAL offers 904L (UNS N08904 / 1.4539) in a wide range of product forms and dimensions:
Plate
Thickness: 5mm to 120mm (3/16″ to 4.7″)
Width: Up to 3300mm (130″)
Length: Up to 12000mm (472″)
Cold Rolled Plate
Thickness: 6mm to 14mm (5/64″ to 5/8″)
Width: Up to 2300mm (90.5″)
Length: Up to 8250mm (325″)
Sheet & Strip
Thickness: 0.5mm to 6mm (0.02″ to 0.25″)
Width: 500mm to 2000mm (20″ to 78″)
Length: Up to 6000mm (236″) or coil form
Bar & Wire
Diameter: 5mm to 100mm (0.2″ to 4″)
Length: Up to 6000mm (236″)
Pipe & Tube
Outside Diameter: 6mm to 325mm (0.24″ to 13″)
Wall Thickness: 0.5mm to 20mm (0.02″ to 0.8″)
Length: Up to 12000mm (472″)
Custom Sizes
Additional dimensions and custom sizes are available upon request.
Fabrication Information
Corrosion Resistance
904L (UNS N08904 / 1.4539) offers exceptional resistance to various types of corrosion:
- Sulfuric Acid Resistance: 904L performs exceptionally well in sulfuric acid environments across a wide range of concentrations and temperatures, outperforming most other high corrosion-resistant grades. This is attributed to its high content of nickel, chromium, molybdenum, and copper additions.
- Phosphoric Acid Resistance: 904L exhibits excellent corrosion resistance in industrial phosphoric acid solutions, significantly better than austenitic grades 316L and 317L. It’s commonly used in phosphoric acid applications, though its performance can be influenced by the presence of impurities like chlorides and fluorides.
- Localized Corrosion: The high chromium and molybdenum contents provide superior resistance to pitting and crevice corrosion compared to 316L and 317L grades, as demonstrated by laboratory tests and field experience.
- Stress Corrosion Cracking: Due to its high nickel and molybdenum content, 904L offers enhanced resistance to stress corrosion cracking compared to standard austenitic materials, performing significantly better than 304L and 316L grades, particularly in high-temperature chloride-containing solutions.
- Intergranular Corrosion: The very low carbon content makes 904L resistant to intergranular corrosion, even in the welded condition.
Welding
904L can be welded using standard processes including TIG/GTAW, MIG/GMAW, SMAW, PAW, and SAW, with the following considerations:
- The grade should be welded with matching filler metal or nickel-based alloys
- Basic electrodes and fluxes are preferable to rutile ones
- Due to its fully austenitic microstructure, certain precautions should be taken:
- Minimize heat input (string bead, limitation of electrode diameter) – preferably limit to 1.5 kJ/mm
- Control interpass temperature to less than 140°C (284°F)
- No preheating or post-heating is required
- Carefully clean and degrease weld areas; descale and clean finished welds
- Use run-on and run-off plates and anti-spatter protection
- Dry electrodes according to manufacturer’s instructions
Machining
Machining 904L requires consideration of the following factors:
- The alloy has a high work hardening rate combined with low sulfur content, making it more difficult to machine than standard grades
- Best results are achieved with slow speeds, sharp tools, positive feeds, powerful machine tools, and ample lubrication
- Cutting tools should be kept engaged with the workpiece and interrupted cuts should be avoided
General machining parameters include:
- Parting off: 10-15 m/min (33-49 ft/min) for high-speed steel tools
- Drilling: 7-11 m/min (23-36 ft/min) for high-speed steel drills
- Milling/profiling: 10-20 m/min (33-66 ft/min) for high-speed steel tools
Why Choose FUSHUN METAL for 904L Super Austenitic Stainless Steel
When your applications demand the superior corrosion resistance and reliability of 904L (UNS N08904 / 1.4539) super austenitic stainless steel, FUSHUN METAL stands as your trusted supply partner:
- Comprehensive inventory of 904L in various product forms including plate, sheet, strip, bar, pipe, and tube
- Premium quality materials sourced from approved mills with full material certification and traceability
- Strict quality control procedures ensuring all products meet or exceed international standards
- Technical expertise to assist with material selection, application advice, and fabrication guidance
- Custom cutting and processing capabilities to meet your specific requirements
- Competitive pricing and reliable delivery schedules
- Long-term experience serving industries that depend on high-performance corrosion-resistant alloys
For applications in sulfuric acid, phosphoric acid, chemical processing, offshore equipment, and other demanding environments where standard stainless steels would fail prematurely, our 904L super austenitic stainless steel provides the ideal solution. Contact our sales team today for a detailed quotation and product information tailored to your specific requirements. Our technical advisors are ready to assist with your material selection to ensure optimal performance and longevity of your critical equipment.
