Key Feature

The High-Alloy Austenitic Corrosion-Resistant Bar Stock. Exceptional resistance to sulfuric acid, phosphoric acid, and chloride solutions, bridging the gap between stainless steels and nickel alloys.

The standard solution for severe corrosive applications, particularly sulfuric and phosphoric acid environments in bar form.

Common Designations

UNS N08904
ASTM B649 (Nickel-Iron-Chromium-Molybdenum-Copper Alloy Bars)
EN 1.4539, X1NiCrMoCu25-20-5
Werkstoff Nr. 1.4539
Alloy 904L
F904L (Wrought product designation)

Often classified as a nickel-iron-chromium alloy due to high nickel content.

Chemical Composition (Typical wt.%)

C: ≤ 0.020
Cr: 19.0 - 23.0Ni: 23.0 - 28.0Mo: 4.0 - 5.0Cu: 1.0 - 2.0Mn: ≤ 2.00
Si: ≤ 1.00
P: ≤ 0.045
S: ≤ 0.035

High nickel (25%) + molybdenum (4.5%) + copper (1.5%) combination provides unique corrosion resistance.

Mechanical Properties

Tensile Strength: ≥ 490 MPa
Yield Strength: ≥ 220 MPa
Elongation: ≥ 35%
Hardness: ≤ 217 HB
Machinability: 40% of B1112 steel
Impact Toughness: Excellent at low temperatures

Good ductility and toughness despite high alloy content.

Physical Properties

Density: 8.00 g/cm³
Melting Range: 1300 - 1390 °C
Thermal Expansion: 15.9 × 10⁻⁶/K (20-100°C)
Thermal Conductivity: 12.5 W/m·K (100°C)
Non-magnetic when annealed

Higher density than conventional stainless steels due to high nickel content.

Available Forms

Rounds: 6mm - 200mm diameter
Squares: 6mm - 100mm
Hexagons: 6mm - 75mm
Flats: Various sizes
Billets: For forging applications
Forgings: Custom forged components

Available in sizes suitable for critical component manufacturing.

Surface Conditions

Hot Rolled: As-rolled surface
Cold Drawn: Bright finish
Centerless Ground: Precision ground
Polished: For specific applications
Peeled/Turned: Improved surface for machining

High-quality finishes available for precision applications.

Corrosion Resistance

Exceptional: PREN*: 33-36
Superior resistance to: Sulfuric acid (all concentrations up to boiling), phosphoric acid, chloride solutions, organic acids, seawater.
Excellent resistance to stress corrosion cracking.

Copper addition enhances resistance to sulfuric acid; high Mo provides chloride resistance.

Machining Characteristics

• Challenging to machine due to work hardening
• High tool wear• Requires rigid setups and powerful equipment
• Good chip control with proper techniques
• Surface finish achievable with care

More difficult to machine than standard stainless steels; requires expertise and proper tooling.

Welding Characteristics

Good weldability with proper procedures
Low carbon prevents sensitizationMatching or overmatched filler metalsHeat input control important
No post-weld annealing required

Similar welding characteristics to other high-alloy austenitic grades.

Temperature Limits

Continuous Service: Up to 400°C (for corrosion)
Higher Temp: Up to 800°C (with property loss)
Cryogenic Service: Excellent to -196°C
Avoid: 600-900°C (precipitation risk)

Good low-temperature toughness; limited high-temperature corrosion service.

Key Standards

ASTM B649 904L: Nickel-Iron-Chromium-Molybdenum-Copper Bars
ASTM B564: Nickel Alloy Forgings
EN 10088-3: Stainless Steel Bars
NORSOK M-630: Offshore materials
ASME SB649: Code Construction

Comprehensive standardization for quality assurance in critical applications.

Common Applications

• Sulfuric Acid Equipment: Pump shafts, valve stems, agitator shafts, reactor components
• Phosphoric Acid Plants: Evaporator parts, pump components, valve bodies, fittings
• Chemical Processing: Reactor agitator shafts, heat exchanger parts, corrosive service components
• Pollution Control: FGD system components, scrubber parts, environmental equipment
• Offshore Oil & Gas: Seawater pump shafts, valve components, topside process parts
• Pulp & Paper: Digester agitator shafts, bleach plant equipment, chemical recovery parts
• Pharmaceutical: Aggressive process equipment, API manufacturing components, tank fittings

Specifically selected for severe corrosive environments, particularly acid services in bar form.