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1. Product Overview
Alloy 500 (UNS N05500, commonly known as Monel K500) is a precipitation-hardenable wrought nickel-copper alloy, strengthened by aluminum and titanium additions. It inherits the outstanding corrosion resistance of Alloy 400, and delivers significantly higher strength and hardness through dedicated age hardening heat treatment. The alloy maintains stable mechanical properties across a wide temperature range, from cryogenic conditions up to approximately 480 °C.
It offers excellent resistance to chloride stress corrosion cracking, pitting and crevice corrosion, and performs reliably in seawater, hydrofluoric acid, caustic alkalis and sour gas environments. With good fabricability and low magnetic permeability, Alloy 500 is widely used for high-strength structural parts, fasteners, shafts and process components in marine, chemical, oil & gas, power and nuclear industries.
2. Grade Standards & Designations
- UNS Number: N05500
- Common Trade Names: Alloy 500, Monel K500
- EN Standard: 2.4375
- Alloy Category: Precipitation-hardenable nickel-copper austenitic alloy
- Key Standards:
- ASTM B865: Bar, rod, wire, forgings and extruded shapes
- ASTM B127: Plate, sheet and strip
- ASTM B163: Seamless pipe and tube
3. Chemical Composition (wt%)
The formulation strictly follows UNS N05500 specifications, ensuring consistent strength performance and corrosion resistance across production batches.
| Element | Content Range | Typical Value |
|---|---|---|
| Ni (Nickel) | ≥ 63.0% | 65.0% |
| Cu (Copper) | 27.0 – 33.0% | 30.0% |
| Al (Aluminum) | 2.30 – 3.15% | 2.70% |
| Ti (Titanium) | 0.35 – 0.85% | 0.60% |
| Fe (Iron) | ≤ 2.00% | 1.00% |
| Mn (Manganese) | ≤ 1.50% | 0.80% |
| Si (Silicon) | ≤ 0.50% | 0.20% |
| C (Carbon) | ≤ 0.18% | 0.10% |
| S (Sulfur) | ≤ 0.010% | 0.005% |
3.1 Strengthening Mechanism
Alloy 500 has a single-phase face-centered cubic (FCC) austenitic matrix. During aging treatment, uniform precipitation of intermetallic Ni₃(Al, Ti) phases acts as the core mechanism for its remarkable strength improvement. It retains the superior corrosion resistance of nickel-copper alloys, outperforming most standard structural alloys in harsh corrosive environments.
4. Physical & Thermal Properties
4.1 Physical Properties
Alloy 500 features low magnetic permeability and remains non-magnetic at temperatures down to -135 °C, making it suitable for electromagnetic equipment and precision electronic devices. It also maintains good ductility and impact toughness at cryogenic temperatures without cold embrittlement.
| Property | Metric Unit | Imperial Unit |
|---|---|---|
| Density | 8.44 g/cm³ | 0.305 lb/in³ |
| Melting Range | 1315 – 1350 °C | 2400 – 2462 °F |
| Modulus of Elasticity | 179 GPa | 26.0 × 10⁶ psi |
| Magnetic Permeability | Low | Low |
4.2 Thermal Properties
| Property | Metric Unit | Imperial Unit |
|---|---|---|
| Thermal Conductivity (@ 20 °C) | 17.4 W/(m·°C) | 10.1 Btu/(ft·h·°F) |
| Mean CTE (20 – 300 °C) | 12.8 × 10⁻⁶ /°C | 7.11 × 10⁻⁶ /°F |
Long-term continuous operating temperature reaches up to 480 °C, with reliable thermal stability under alternating hot and cold conditions.
5. Mechanical Properties
Alloy 500 is a typical precipitation-hardenable alloy. Solution-annealed material has excellent ductility for forming and rough machining; strength and hardness can be significantly enhanced via aging treatment. Cold working before aging can achieve further strength improvement.
| Property | Solution Annealed | Aged Condition |
|---|---|---|
| Tensile Strength | 550 – 760 MPa (80 – 110 ksi) | 1000 – 1310 MPa (145 – 190 ksi) |
| 0.2% Offset Yield Strength | ≥ 275 MPa (≥ 40 ksi) | ≥ 790 MPa (≥ 115 ksi) |
| Elongation | ≥ 25% | ≥ 12% |
| Brinell Hardness (HB) | 140 – 180 | 280 – 360 |
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-resistant parts |
| Alloy 400 | Hydrofluoric acid, alkali, seawater | Medium-High | Good | Medium-strength corrosion components |
| Alloy 500 (UNS N05500) | Hydrofluoric acid, alkali, sour gas | Ultra-High | Fair | High-strength corrosion-resistant parts |
| Hastelloy C276 | Severe corrosive media | Medium | Fair | Extreme corrosion service |
7. Advantages & Application Limitations
7.1 Key Performance Advantages
- Inherits excellent corrosion resistance of nickel-copper alloys, resistant to seawater, HF, caustic alkali and sour gas
- Remarkable strength gain after precipitation hardening, far higher than Alloy 400 and conventional stainless steels
- Stable mechanical properties from cryogenic temperature up to 480 °C
- Low magnetic permeability, applicable for electromagnetic and precision electronic equipment
- Good fatigue resistance, ideal for dynamic load components such as shafts and fasteners
- Long service life under combined corrosion and high-load working conditions
7.2 Application Limitations
Not recommended for strong oxidizing media such as concentrated nitric acid and concentrated chromic acid. In addition, fully aged material has a certain risk of stress corrosion cracking in static seawater, which requires attention in design and application.
8. Fabrication Guidelines
8.1 Heat Treatment
- Solution Annealing (pre-treatment for aging): Heat to 980 – 1050 °C, hold sufficiently, then water quench or oil quench to obtain a supersaturated solid solution.
- Age Hardening: Hold at 480 – 620 °C for 8 – 16 hours, followed by air cooling. Precipitation of Ni₃(Al, Ti) phases achieves maximum strength. Two-step aging is optional for optimized comprehensive performance.
- Stress Relieving: Perform at 550 – 650 °C after machining or welding to eliminate residual stress.
8.2 Machining
The alloy shows an obvious work-hardening effect. Rough machining is recommended under solution-annealed condition. Use cemented carbide tools, low cutting speed and sufficient heavy-duty cutting fluid. Finish machining shall be arranged after aging to guarantee dimensional accuracy.
8.3 Welding
GTAW (TIG) and GMAW (MIG) are preferred processes; SMAW is also acceptable. Matching filler metal: ERNiCu-7 / ENiCu-7. Thoroughly remove oil, grease and oxides on weld joints before welding. Preheat thick sections to 150 – 200 °C, and keep interpass temperature below 150 °C. Complete welding before aging treatment; post-weld stress relief is mandatory for critical parts. Oxyacetylene welding is prohibited.
9. Product Forms & Specifications
We supply a full range of wrought Alloy 500 (UNS N05500) products with standard and custom dimensions:
- Bars & Wires: Round, square, hex bars; diameter 6 – 320 mm
- Plates & Sheets: Thickness 2 – 90 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: Propeller shafts, pump shafts, offshore platform fasteners, seawater pipeline components
- Chemical Processing: High-strength valves, agitators, equipment parts for hydrofluoric acid and alkali service
- Oil & Gas: Sour gas well tools, downhole components, high-pressure pipeline fittings
- Power & Nuclear: High-strength fasteners, steam system structural parts
- General Machinery: Springs, chains, magnetic-isolation components, fatigue-resistant parts
11. Frequently Asked Questions (FAQ)
Q: Is Alloy 500 (UNS N05500) magnetic?
A: It has low magnetic permeability and remains non-magnetic at temperatures above -135 °C, suitable for electromagnetic and precision sensing applications.
Q: Can Alloy 500 be heat treated for higher strength?
A: Yes. It is a precipitation-hardenable alloy. Standard aging treatment can greatly improve its strength and hardness.
Q: What is the maximum continuous operating temperature of Alloy 500?
A: Its long-term continuous service temperature reaches up to 480 °C.
Q: What is the difference between Alloy 500 and Alloy 400?
A: Alloy 500 adds aluminum and titanium for precipitation hardening, delivering much higher strength and hardness. Alloy 400 offers better ductility, lower cost and is used for general structural applications.
Q: What delivery conditions are available?
A: Solution annealed, cold worked and aged conditions are all available, customizable according to 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.
