Monel 400 – UNS N04400
Solid-solution-strengthened nickel-copper alloy
Single-phase Ni-Cu alloy (~65/30), with excellent resistance to flowing seawater, brines, alkalis and hydrofluoric acid at all concentrations. Moderate mechanical strength, which increases only by cold work. It is slightly magnetic at room temperature.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N04400 |
| W.Nr./EN | 2.4360 – NiCu30Fe |
| DIN | NiCu30Fe |
| JIS | NW4400 (JIS H 4551 NCuP) |
| Trade names | Monel 400 (Special Metals), Nicorros (VDM), Alloy 400 |
| Others | GB NiCu28-2.5-1.5; QQ-N-281; AMS 4544 (plate), AMS 4675 (bar) |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM B164 |
| Forging | ASTM B564 |
| Plate | ASTM B127 |
| Tube | ASTM B165 (seamless), B163 (exchanger) |
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 |
| Plate (> 10 mm, width ≥ 600 mm) | 7506.20.00 | 7506.20 | 7506.20.3000 | 7506 20 00 |
| Seamless pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Welded pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 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 B164 / B564 (UNS N04400)
| Element | Range (%) |
|---|---|
| Ni (+Co) | ≥ 63.0 |
| Cu | 28.0 – 34.0 |
| Fe | ≤ 2.5 |
| Mn | ≤ 2.0 |
| C | ≤ 0.3 |
| Si | ≤ 0.5 |
| S | ≤ 0.024 |
Mechanical properties
annealed (ASTM B564 / B164)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 172 MPa |
| Tensile strength | ≥ 483 MPa |
| Elongation | ≥ 35% |
| Hardness (typical, annealed) | ≈ 110 – 150 HB |
Typical physical properties
| Property | Value |
|---|---|
| Density | 8.80 g/cm³ |
| Melting range | 1,300 – 1,350 °C |
| Modulus of elasticity | 179 GPa |
| Thermal conductivity (20 °C) | 21.8 W/m·K |
| Thermal expansion (20–100 °C) | 13.9 µm/m·K |
| Curie temperature (typical) | ≈ 20 – 50 °C |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | From cryogenic up to ~480 °C in pressure equipment; in oxidizing atmospheres, up to ~540 °C. Sulfur-bearing atmospheres attack the alloy at elevated temperature. |
| Heat treatment | Annealing at ≈ 870 – 980 °C for a few minutes, with rapid cooling. Stress relief at ≈ 540 – 565 °C for 1 – 2 h, with slow cooling. Stress equalization at ≈ 300 °C for 3 h. Not age hardenable. |
| Welding | Good weldability. Consumables: AWS A5.14 ERNiCu-7 (FM 60 type) and AWS A5.11 ENiCu-7 (190 type). |
| Machining | 'Gummy' material in the annealed condition; machines better cold drawn. Use a sharp, positive-rake tool. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Pump and propeller shafts, valves and fasteners in seawater
- Hydrofluoric acid (HF) alkylation units
- Seawater-cooled exchangers and condensers
- Boiler feedwater heaters
- Tops of petroleum distillation columns
- Brine and caustic soda tanks and piping
Alternatives: Monel K500 when 2 to 3 times more mechanical strength is needed; Monel R-405 for automatic machining; 70/30 copper-nickel in seawater at lower cost; C276 in aerated HF or with oxidizers.
Monel 400: complete guide
What Monel 400 is
Monel 400 belongs to the family of nickel alloys, in the nickel-copper group. Nickel and copper form a solid solution in any proportion, so the alloy has a single phase, does not harden by heat treatment and gains strength only by cold work. Iron and manganese are secondary elements; titanium and aluminum are not part of Monel 400 but of Monel K-500, which is therefore precipitation hardenable.
Welding and machining
Weldable by TIG, MIG and covered electrode with ERNiCu-7 consumables, without preheating or post-weld treatment, provided the surfaces are free of sulfur, lead and oils. Machining produces sticky chips and requires sharp tools, positive feed and abundant coolant.
Corrosion and limits of use
Monel 400 resists flowing seawater, brines, steam and saline solutions, hydrofluoric acid at all concentrations up to boiling, fluorine and dilute, deaerated sulfuric and hydrochloric acids, as well as alkaline media. It suffers pitting and crevice corrosion in stagnant seawater, is attacked by oxidizing media such as nitric acid and ferric chloride, and may suffer stress corrosion cracking in aerated hydrofluoric acid. For seawater with high mechanical loading, Inconel 625 and the super duplex grades are the alternatives.
Applications
Pump and propeller shafts, valve stems and seats, seawater heat exchangers and condensers, marine fasteners and fittings, hydrofluoric acid production and alkylation equipment, fresh water and fuel tanks, petroleum distillation units, electrical components and springs.
Monel 400 or K-500: which to choose
The two alloys have the same nickel-copper base and the same corrosion resistance. K-500 receives aluminum (2.30 – 3.15%) and titanium (0.35 – 0.85%) and is age hardened: yield ≥ 690 MPa and tensile ≥ 965 MPa, versus ≥ 172 MPa and ≥ 483 MPa for 400. Use 400 in exchangers, tanks, piping, pumps and valves, where corrosion is the criterion. Use K-500 in shafts, springs, fasteners and parts subject to wear. K-500 is also non-magnetic down to ≈ −100 °C.
The Monel family
Monel is a Special Metals trademark for a family of nickel-copper alloys. The most used are 400, K-500 and R-405, a sulfur-bearing version for automatic machining. Besides marine, chemical, petroleum and food processing uses, Monel appears in small parts exposed to corrosion, such as the piston valves of trumpets.
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 400?
Per ASTM B164 / B564 (UNS N04400): Ni (+Co) ≥ 63.0; Cu 28.0 – 34.0; Fe ≤ 2.5; Mn ≤ 2.0; C ≤ 0.3; Si ≤ 0.5.
Which standards cover Monel 400?
Bar: ASTM B164. Forging: ASTM B564. Plate: ASTM B127. Tube: ASTM B165 (seamless), B163 (exchanger).
Up to what temperature can Monel 400 be used?
From cryogenic up to ~480 °C in pressure equipment; in oxidizing atmospheres, up to ~540 °C. Sulfur-bearing atmospheres attack the alloy at elevated temperature.
Which materials can replace Monel 400?
Monel K500 when 2 to 3 times more mechanical strength is needed; Monel R-405 for automatic machining; 70/30 copper-nickel in seawater at lower cost; C276 in aerated HF or with oxidizers.
What is the difference between Monel 400 and Monel K-500?
K-500 has aluminum and titanium and is age hardened: yield ≥ 690 MPa versus ≥ 172 MPa for 400. Corrosion resistance is the same. 400 serves where corrosion rules; K-500, where mechanical or wear strength is also required.
When should Monel be used instead of stainless steel?
In flowing seawater, brines, hydrofluoric acid and alkalis, where ordinary stainless suffers pitting or stress corrosion cracking. In stagnant seawater and oxidizing media, such as nitric acid and ferric chloride, Monel is not indicated.
Can Monel 400 be used at low temperature?
Yes. It keeps its toughness from cryogenic up to about 480 °C in pressure equipment, with no ductile-brittle transition.
