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1. Product Overview
Alloy 400 (UNS N04400) is a solid-solution strengthened nickel-copper wrought alloy, widely used as a cost-effective option for moderate to severe corrosive service. It significantly outperforms 316L stainless steel in seawater, hydrofluoric acid and concentrated caustic environments, while offering better fabricability than premium Hastelloy grades.
This alloy delivers excellent resistance to chloride stress corrosion cracking, pitting and crevice corrosion. With good machinability, formability and weldability, it is extensively specified for critical equipment in marine, chemical, oil & gas, power and nuclear industries.
2. Grade Standards & Designations
- UNS Number: N04400
- Common Trade Names: Alloy 400, Monel 400
- EN Standard: 2.4360
- Alloy Category: Nickel-copper solid-solution austenitic alloy
- Key Standards: ASTM B164 (rod/bar/wire), ASTM B165 (seamless pipe/tube)
3. Chemical Composition (wt%)
The formulation strictly follows UNS N04400 specifications, ensuring consistent corrosion resistance and mechanical stability across production batches.
| Element | Content Range | Typical Value |
|---|---|---|
| Ni (Nickel) | ≥ 63.0% | 65.0% |
| Cu (Copper) | 28.0 – 34.0% | 31.0% |
| Fe (Iron) | ≤ 2.50% | 1.20% |
| Mn (Manganese) | ≤ 2.00% | 1.00% |
| Si (Silicon) | ≤ 0.50% | 0.20% |
| C (Carbon) | ≤ 0.30% | 0.10% |
| S (Sulfur) | ≤ 0.024% | 0.01% |
3.1 Core Alloying Logic
- Nickel: Forms the austenitic matrix, provides fundamental caustic corrosion and chloride SCC resistance, and ensures non-magnetic property.
- Copper: The key element for superior hydrofluoric acid and seawater corrosion resistance, and improves alloy formability.
- Iron & Manganese: Enhance structural strength and hot workability at controlled low content.
4. Physical & Thermal Properties
4.1 Physical Properties
Alloy 400 (UNS N04400) maintains a stable single-phase austenitic structure under all heat treatment conditions, remaining fully non-magnetic across its entire service temperature range.
| Property | Metric Unit | Imperial Unit |
|---|---|---|
| Density | 8.83 g/cm³ | 0.319 lb/in³ |
| Melting Range | 1300 – 1350 °C | 2372 – 2462 °F |
| Modulus of Elasticity | 179 GPa | 26.0 × 10⁶ psi |
| Magnetic Property | Non-magnetic | Non-magnetic |
It retains excellent ductility and impact toughness at cryogenic temperatures down to -196 °C without cold embrittlement, suitable for low-temperature engineering and cryogenic storage systems.
4.2 Thermal Properties
| Property | Metric Unit | Imperial Unit |
|---|---|---|
| Thermal Conductivity (@ 20 °C) | 21.8 W/(m·°C) | 12.6 Btu/(ft·h·°F) |
| Mean CTE (20 – 300 °C) | 13.9 × 10⁻⁶ /°C | 7.72 × 10⁻⁶ /°F |
| Mean CTE (300 – 500 °C) | 15.2 × 10⁻⁶ /°C | 8.44 × 10⁻⁶ /°F |
Continuous operating temperature range: -196 °C to 400 °C, with excellent thermal stability for heat exchangers, steam piping and wide-temperature process equipment.
5. Mechanical Properties
Alloy 400 (UNS N04400) is a non-heat-treatable alloy; strength can only be improved via cold working. Standard supply condition is solution annealed for optimum ductility.
| Property | Solution Annealed | Cold Worked |
|---|---|---|
| Tensile Strength | ≥ 480 MPa (69.6 ksi) | 700 – 900 MPa (101.5 – 130.5 ksi) |
| 0.2% Offset Yield Strength | ≥ 195 MPa (28.3 ksi) | 550 – 750 MPa (79.8 – 108.8 ksi) |
| Elongation | ≥ 35% | – |
| Reduction of Area | ≥ 45% | – |
| Charpy V-Notch Impact | ≥ 110 J (81 ft-lb) | – |
| Brinell Hardness (HB) | 135 – 179 | – |
Strength increases proportionally with cold working degree; custom cold-worked grades are available upon request.
6. Performance Comparison & Alloy Positioning
| Alloy Grade | Dominant Corrosion Resistance | Strength Level | Fabricability | Primary Application |
|---|---|---|---|---|
| 316L Stainless Steel | Oxidizing & chloride media | Medium | Excellent | General corrosion components |
| Alloy 400 (UNS N04400) | Hydrofluoric acid, alkali, seawater | Medium-High | Good | Cost-effective nickel-copper structural parts |
| Alloy K500 | General corrosive media | High | Fair | Age-hardenable high-strength components |
| Alloy 20 | Sulfuric acid & organic acid | Medium | Good | Acid-resistant process equipment |
| Hastelloy C276 | Severe corrosive media | Medium | Fair | Ultra-severe corrosion service |
7. Advantages & Application Limitations
7.1 Key Performance Advantages
- Industry-leading resistance to hydrofluoric acid, concentrated caustic alkalis and seawater
- Excellent resistance to pitting, crevice corrosion and chloride SCC
- Outstanding toughness from cryogenic temperatures up to 400 °C
- Inherent non-magnetic property for electromagnetic and precision devices
- Good weldability and formability for complex component fabrication
- Long service life and competitive total cost of ownership
7.2 Application Limitations
Not recommended for strong oxidizing environments such as concentrated nitric acid, concentrated chromic acid and high-temperature oxidizing flue gas, as corrosion rate rises significantly under these conditions.
8. Fabrication Guidelines
8.1 Heat Treatment
- Full Annealing (standard supply): 870 – 980 °C with proper soaking, air/water quenched; restores ductility and relieves residual stress.
- Stress Relieving: 550 – 700 °C after machining/welding; strict temperature control required to avoid property degradation.
Note: Alloy 400 (UNS N04400) cannot be age hardened. Cold working is the only valid method to improve strength.
8.2 Machining
The alloy has an obvious work-hardening tendency and tends to form built-up edge during cutting. Cemented carbide tools are recommended, with low cutting speed, moderate feed rate and sulfurized cutting fluid to minimize tool wear.
8.3 Welding
GTAW (TIG) and GMAW (MIG) are preferred processes, with matching filler metal ERNiCu-7. Remove oil, grease and surface oxides before welding. Preheating is unnecessary; interpass temperature shall be kept below 150 °C. Post-weld stress relief is recommended for tight-tolerance components.
9. Product Forms & Specifications
We supply a complete range of wrought Alloy 400 (UNS N04400) products with standard and custom dimensions:
- Bars & Wires: Round, square, hex bars; diameter 6 – 300 mm
- Plates & Sheets: Thickness 2 – 80 mm; custom cutting available
- Pipes & Fittings: Seamless/welded pipes, elbows, tees, reducers, caps; DN15 – DN600, custom wall thickness
- Flanges & Forgings: WN, SO, blind flanges and custom structural forgings
- Welding consumables & industrial fasteners
All products come with full material test reports and EN 10204 3.1 mill certificates.
10. Typical Applications
- Marine Engineering: Seawater pipelines, marine valves, pump shafts, heat exchangers, splash zone structures
- Chemical Processing: Hydrofluoric acid equipment, alkali evaporators, sulfuric acid pipelines, desulfurization agitators
- Oil & Gas: Downhole tools, gathering pipelines, sour gas components, crude distillation units
- Power & Nuclear: Boiler feedwater heaters, steam tubing, nuclear auxiliary corrosion parts
- General Industry: Heat exchangers, non-magnetic sensor housings, high-strength fasteners
11. Frequently Asked Questions (FAQ)
Q: Is Alloy 400 (UNS N04400) magnetic?
A: No. Alloy 400 (UNS N04400) remains completely non-magnetic under all heat treatment and service conditions, ideal for electromagnetic and precision sensing applications.
Q: Can Alloy 400 (UNS N04400) be hardened by heat treatment?
A: No. This alloy cannot be precipitation hardened. Cold working is the only way to increase strength, while annealing will soften the material.
Q: What media is Alloy 400 (UNS N04400) most suitable for?
A: It is the preferred material for hydrofluoric acid, high-concentration caustic soda, seawater and non-oxidizing chloride solutions.
Q: What is the difference between Alloy 400 and Alloy K500?
A: Alloy K500 is the age-hardenable version with higher strength but lower ductility. Alloy 400 offers better toughness and lower cost for general structural applications.
Q: What supply conditions are available?
A: Solution annealed condition is standard; cold-worked grades with different strength levels are available for high-strength requirements.
Related resources: Browse our full range of nickel alloy pipe fittings & seamless tubes, or learn more about our manufacturing capabilities on the C&N YouTube channel for product testing and factory updates.
