Monel K-500 – UNS N05500
Precipitation-hardenable nickel-copper alloy
Ni-Cu alloy with aluminum and titanium, hardened by precipitation of γ′ Ni₃(Al,Ti). It keeps the corrosion resistance of Monel 400 in seawater, with a yield strength about 3 times higher. It is non-magnetic down to about −100 °C, which is why it is used in directional drilling tools.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N05500 |
| W.Nr./EN | 2.4375 – NiCu30Al |
| DIN | NiCu30Al |
| Trade names | Monel K-500 (Special Metals), Nicorros Al (VDM), Alloy K-500 |
| Others | QQ-N-286; AMS 4676 |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM B865; AMS 4676 |
| Forging | ASTM B865; AMS 4676 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Hot-rolled bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Flange and fitting | 7507.20.00 | 7507.20 | 7507.20.0000 | 7507 20 00 |
Tariff class: nickel alloy (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM B865 (UNS N05500)
| Element | Range (%) |
|---|---|
| Ni (+Co) | ≥ 63.0 |
| Cu | 27.0 – 33.0 |
| Al | 2.30 – 3.15 |
| Ti | 0.35 – 0.85 |
| Fe | ≤ 2.0 |
| Mn | ≤ 1.5 |
| C | ≤ 0.18 (ASTM B865) |
| Si | ≤ 0.5 |
| S | ≤ 0.01 |
Mechanical properties
hot rolled + aged (ASTM B865)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 690 MPa |
| Tensile strength | ≥ 965 MPa |
| Elongation | ≥ 20% |
| Hardness | ≥ 27 HRC (≈ 265 HB) |
| Max. hardness (NACE MR0175/ISO 15156) | ≤ 35 HRC |
Typical physical properties
| Property | Value |
|---|---|
| Density | 8.44 g/cm³ |
| Melting range | 1,315 – 1,350 °C |
| Modulus of elasticity | 179 GPa |
| Thermal conductivity (20 °C) | 17.4 W/m·K |
| Thermal expansion (20–100 °C) | 13.7 µm/m·K |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | From cryogenic up to ~480 °C (typical), keeping the aged properties. Non-magnetic down to ≈ −100 °C. |
| Heat treatment | Solution treatment (if needed) at 980 – 1,040 °C. Aging of annealed material: 593 – 607 °C for 16 h, furnace cooling at 8 – 14 °C/h to 480 °C and then air. Cold-worked material: shorter times or a temperature of ≈ 527 – 538 °C. Overaged material must be solution treated before aging again. |
| Welding | Weld in the annealed condition and age afterwards. Usual consumable AWS ERNiCu-7 (FM 60), whose weld metal does not harden: the joint is weaker than the aged base metal. |
| Machining | Rough machine in the annealed condition and finish after aging (the material hardly distorts). Machines better than Monel 400. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Pump shafts and marine propellers
- Fasteners, springs and chains for marine service
- Non-magnetic drill collars and MWD/LWD tools
- Impellers and valve internals
- Doctor blades in pulp and paper
- Sensors and instrumentation
Alternatives: Monel 400 when mechanical strength is not critical; 718/725 in high-strength sour (H₂S) service; Nitronic 50 or duplex for lower-cost marine shafts. Caution: under cathodic protection, aged K500 is susceptible to hydrogen embrittlement.
Monel K-500: complete guide
What Monel K-500 is
Monel K-500 belongs to the family of nickel alloys, in the precipitation-hardenable nickel-copper group. The base is that of Monel 400; the added aluminum and titanium form, during aging, the finely dispersed gamma-prime Ni3(Al,Ti) precipitate, which raises strength and hardness.
Heat treatment
Solution treatment is done at about 980 °C with water quenching; aging at 593 – 607 °C for 16 hours with slow furnace cooling to about 480 °C, in a sulfur-free atmosphere. Parts cold worked before aging reach even higher strength. Dustre performs these cycles in its own furnaces as part of its heat treatment service, with a certificate of the delivered condition.
Corrosion and limits of use
Corrosion resistance is that of Monel 400: excellent in flowing seawater, brines, steam, hydrofluoric acid and reducing media, limited in stagnant seawater and oxidizing media. The higher hardness improves resistance to erosion and cavitation. The alloy is non-magnetic down to about −100 °C, which sets it apart from Monel 400 and makes it suitable for downhole tools and instruments. For H2S, NACE MR0175 limits hardness to 35 HRC; use goes up to about 480 °C.
Applications
Seawater pump shafts and impellers, valve stems and seats, marine springs and fasteners, drill collars and non-magnetic downhole tools, downhole measuring instruments, blades and scrapers for the pulp industry, process equipment components for fluorine and hydrofluoric acid.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing or annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of Monel K-500?
Per ASTM B865 (UNS N05500): Ni (+Co) ≥ 63.0; Cu 27.0 – 33.0; Al 2.30 – 3.15; Ti 0.35 – 0.85; Fe ≤ 2.0; Mn ≤ 1.5.
Which standards cover Monel K-500?
Bar: ASTM B865; AMS 4676. Forging: ASTM B865; AMS 4676.
Up to what temperature can Monel K-500 be used?
From cryogenic up to ~480 °C (typical), keeping the aged properties. Non-magnetic down to ≈ −100 °C.
Which materials can replace Monel K-500?
Monel 400 when mechanical strength is not critical; 718/725 in high-strength sour (H₂S) service; Nitronic 50 or duplex for lower-cost marine shafts. Caution: under cathodic protection, aged K500 is susceptible to hydrogen embrittlement.
