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When is Monel K-500 used instead of Monel 400?
Short answer
Monel K-500 is used when a part needs much higher strength than Monel 400 can give, such as pump shafts, impellers, fasteners and oil-well tools. Aluminium and titanium let K-500 be age-hardened to about three times the yield strength of 400, while corrosion resistance stays similar.
Monel 400 vs Monel K-500 at a glance
| Property | Monel 400 | Monel K-500 |
|---|---|---|
| UNS | N04400 | N05500 |
| EN | 2.4360 | 2.4375 |
| Family | Nickel-copper (Ni-Cu) alloy | Nickel-copper (Ni-Cu) alloy |
| C (%) | 0.3 max | 0.25 max |
| Ni (%) | 63.0 min | 63.0 min |
| Cu (%) | 28.0 – 34.0 | 27.0 – 33.0 |
| Ti (%) | — | 0.35 – 0.85 |
| Al (%) | — | 2.30 – 3.15 |
| Fe (%) | 2.5 max | 2.0 max |
| Tensile strength | 483 MPa (70 ksi) | 965 MPa (140 ksi) |
| Yield strength | 193 MPa (28 ksi) | 690 MPa (100 ksi) |
| PREN | — | — |
| Density | 8.8 g/cm³ | 8.44 g/cm³ |
| Magnetic | Only slightly magnetic at room temperature. | Only slightly magnetic at room temperature. |
| Typical use | HF alkylation units in refineries | Marine pump and propeller shafts |
Which should you choose?
There's no universal "winner": the right choice depends on service conditions, codes and cost. Share your conditions with us for a recommendation.
Hydrogen and high hardness
Age-hardened K-500 can be susceptible to hydrogen embrittlement, for example under cathodic protection in seawater at high hardness. Projects often limit hardness or require specific heat treatments for marine fasteners.
Where 400 remains the standard
Alloy 400 is the usual choice for seawater piping, hydrofluoric acid plant, brine heaters and vessel cladding, where weldability and corrosion resistance matter more than strength.
Products in both grades
Related guides, comparisons and articles
Frequently asked questions
Which specification covers K-500 bar?
ASTM B865, ordered in the annealed or aged condition as required.
Is K-500 magnetic?
It is essentially non-magnetic at room temperature, which makes it useful for some instrument and marine applications.
What is the main difference between Monel 400 and Monel K-500?
K-500 adds aluminium and titanium so it can be age-hardened to about three times the yield strength of 400. Corrosion resistance is similar, although K-500 is more susceptible to hydrogen embrittlement in some conditions.
When should I choose Monel 400?
Piping, vessels and HF-acid equipment.
When should I choose Monel K-500?
Pump shafts, fasteners and high-strength marine parts.
Can Monel 400 replace Monel K-500?
Only when the design, code and specification allow it. Strength, corrosion resistance and temperature limits differ, so substitution must be approved by the design authority.