Monel 400 and Monel K-500 are the two basic grades of the nickel–copper alloys. Their corrosion behaviour is almost identical; the difference is in strength.
When aluminium and titanium are added
Monel 400 is a simple nickel–copper alloy: nickel min 63.0%, copper 28.0–34.0%. It hardens only by cold working; its strength cannot be raised by heat treatment.
In Monel K-500, 2.30–3.15% aluminium and 0.35–0.85% titanium are added to the same nickel–copper backbone. During the ageing treatment these two elements combine with nickel to form fine precipitates and make the alloy precipitation hardening. The result is several times the strength of 400 — without giving up corrosion resistance.
Another practical difference: Monel K-500 is non-magnetic and non-sparking; that property makes it the preferred choice for hand tools and pump shafts working in explosive atmospheres.
The carbon content is lowered as well: max 0.30% in 400 against max 0.25% in K-500.
Comparison in numbers
| PROPERTY | Monel 400 | Monel K-500 |
|---|---|---|
| Nickel (Ni+Co) | min 63.0% | min 63.0% |
| Copper (Cu) | 28.0 – 34.0% | 27.0 – 33.0% |
| Aluminium (Al) | — | 2.30 – 3.15% |
| Titanium (Ti) | — | 0.35 – 0.85% |
| Iron (Fe) | max 2.50% | max 2.00% |
| Carbon (C) | max 0.30% | max 0.25% |
| Manganese (Mn) | max 2.00% | max 1.50% |
| Silicon (Si) | max 0.50% | max 0.50% |
| Sulphur (S) | max 0.024% | max 0.01% |
| Hardening | Cold working | Precipitation (ageing) |
| UNS | N04400 | N05500 |
| W.Nr (DIN/EN) | 2.4360 · 2.4361 | 2.4375 |
| AMS | 4544 · 4574 · 4675 | 4676 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Monel 400 is sufficient — seawater piping and valves, heat exchanger tubes, desalination plants, hydrofluoric acid equipment, chemical process vessels. Its weldability and formability are excellent.
Monel K-500 is required — pump and valve shafts, submarine and ship shafts, drilling cable components, non-sparking hand tools, high-strength fasteners. If the specification calls out AMS 4676, 400 is not an acceptable substitute.
Note: under certain conditions K-500 is susceptible to hydrogen embrittlement; in cathodically protected marine applications its hardness level is limited.
Neighbouring alloys
Where pure nickel is required there are Nickel 200 and Nickel 201, and for nickel–chromium alloys with high chloride resistance, Inconel 625 and Incoloy 825.
Technical datasheets
Monel 400 — chemical composition, mechanical values, standard equivalents
Monel K-500 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.