Alloy 400 is a solid-solution nickel–copper alloy (approximately 67% nickel, 30% copper) — the first of the corrosion-resistant nickel alloys, developed in 1905. This datasheet presents the material within the American (ASTM / ASME / SAE-AMS / UNS) standard system.
It combines good mechanical properties with excellent resistance to a wide range of corrosive media. It is one of the few materials that resists hydrofluoric acid and fluorine, and is a benchmark material for seawater and marine service, where it resists flowing seawater, brackish water and brine. It also resists reducing acids such as sulphuric and hydrochloric under non-oxidising (de-aerated) conditions, alkalis, salts and most organic acids, and is highly resistant to chloride-ion stress-corrosion cracking. Being free of chromium, it is not suited to strongly oxidising environments.
The alloy is not age-hardenable; it is strengthened only by cold work. It retains strength and toughness from sub-zero temperatures to about 400 °C with no ductile-to-brittle transition, and is readily fabricated and welded. Typical applications include marine and offshore equipment (propeller shafts, seawater piping, pumps and valves), chemical and hydrocarbon processing, heat exchangers and feedwater heaters, crude-petroleum stills, fasteners and springs. It is listed in NACE MR0175 / ISO 15156 for sour service.
Values per manufacturer (Special Metals / VDM) data, annealed condition.
| Property | Value | Unit |
|---|---|---|
| Density | 8.80 | g/cm³ |
| Melting range | 1300–1350 | °C |
| Young's modulus (20 °C) | 179 | GPa |
| Specific heat capacity (20 °C) | 427 | J/kg·K |
| Thermal conductivity (20 °C) | 21.8 | W/m·K |
| Electrical resistivity (20 °C) | 0.51 | µΩ·m |
| Coefficient of thermal expansion (20–100 °C) | 13.9 | µm/m·°C |
| Curie temperature | ~20–50 | °C |
| Magnetic response | Ferromagnetic near room temperature | — |
| Maximum service temperature | ~480 (ASME); to ~540 in some service | °C |
Limiting composition per ASTM B164 (UNS N04400).
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Nickel (+ Cobalt) | Ni | 63.0 | — | Base element; corrosion resistance (typ. ~67%) |
| Copper | Cu | 28.0 | 34.0 | Primary alloying element; reducing-acid + seawater resistance |
| Iron | Fe | 1.0 | 2.5 | Controlled (typ. ~1.5) |
| Manganese | Mn | — | 2.0 | Deoxidiser |
| Carbon | C | — | 0.3 | Controlled |
| Silicon | Si | — | 0.5 | Deoxidiser |
| Sulphur | S | — | 0.024 | Residual impurity |
Note: a solid-solution Ni-Cu alloy; the high nickel content gives chloride-SCC resistance and the copper gives resistance to reducing acids and seawater.
Typical room-temperature properties, annealed condition.
| Property | Value | Source |
|---|---|---|
| Ultimate tensile strength | 480–585 MPa | Annealed |
| 0.2% proof strength (yield) | 170–345 MPa | Annealed |
| Elongation at break | 35–40 % | Annealed |
| Hardness | ~110–150 HB | Annealed |
The alloy is solid-solution (not age-hardenable) and is strengthened by cold work, which can substantially raise the tensile and yield strengths. It retains strength and toughness from cryogenic temperatures to about 400 °C with no ductile-to-brittle transition. Values are typical; confirm against the mill test certificate for each delivery.
| Environment | Performance | Notes |
|---|---|---|
| Seawater / brackish water / brine | Outstanding | Benchmark marine material; resists flowing seawater |
| Hydrofluoric acid / fluorine | Outstanding | One of few materials resistant to HF and fluorine |
| Sulphuric / hydrochloric acid (reducing) | Very Good | Under non-oxidising (de-aerated) conditions |
| Alkalis | Excellent | Good resistance to caustic |
| Salts / most organic acids | Excellent | Broad resistance |
| Chloride stress-corrosion cracking | Outstanding | High nickel content |
| Sour service (H₂S) | Good | NACE MR0175 / ISO 15156 |
| Stagnant seawater | Caution | May pit under stagnant conditions |
| Oxidising media (nitric acid, oxidising salts) | Poor | No chromium — avoid |
A solid-solution nickel–copper alloy; not age-hardenable. Heat treatment is for annealing / stress relief only; strengthening is by cold work.
Anneal Temperature: 700–900 °C, time depending on section and prior cold work, followed by appropriate cooling Purpose: softening and recrystallisation after cold work.
Stress relief of cold-worked material can be carried out at lower temperatures. The alloy has no ductile-to-brittle transition and retains toughness to cryogenic temperatures.
Readily welded by common processes and also brazed and soldered. The alloy is easily fabricated and retains good ductility in the as-welded condition.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG · GMAW / MIG | Excellent | AWS A5.14 ERNiCu-7 (Monel Filler Metal 60) |
| SMAW / stick | Good | AWS A5.11 ENiCu-7 (Monel Electrode 190) |
Keep joints clean and free of contaminants. Welds should be made on clean, grease-free surfaces; the alloy's good weldability makes it well suited to fabricated marine and process equipment.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Condition | Machines best cold-drawn or cold-drawn + stress-relieved |
| Work hardening | Work-hardens; rigid setup, sharp tooling, positive rake |
| Coolant | Flood coolant recommended |
Forming Processes
| Process | Notes |
|---|---|
| Hot forming | Standard hot-working practice for Ni-Cu alloys |
| Cold forming | Readily formed; work-hardens (strengthening by cold work) |
| Annealing | 700–900 °C after heavy cold work |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Marine / offshore | Propeller shafts, seawater piping, pumps, valves, fittings | Seawater + chloride-SCC resistance |
| Chemical processing | Reactors, heat exchangers, piping for reducing acids | Sulphuric/hydrochloric (reducing) + HF resistance |
| Oil and gas | Sour-service hardware, crude-petroleum stills | H₂S resistance (NACE MR0175) |
| Hydrofluoric acid | HF production and handling equipment | One of few HF-resistant materials |
| Power / process | Feedwater heaters, heat exchangers | Corrosion resistance + thermal performance |
| Fasteners / springs | Bolts, fasteners, springs | Strength + corrosion resistance |
| Product Form | ASTM Standard | ASME Code | AMS |
|---|---|---|---|
| Rod, bar and wire | ASTM B164 | ASME SB-164 | AMS 4730 |
| Plate, sheet and strip | ASTM B127 | ASME SB-127 | AMS 4544 |
| Seamless pipe and tube | ASTM B163 / B165 | ASME SB-163 / SB-165 | — |
| Forgings | ASTM B564 | ASME SB-564 | AMS 4675 |
| Fittings | ASTM B366 | ASME SB-366 | — |
| Fasteners | ASTM F467 / F468 | — | — |
| Welding consumables | AWS A5.14 ERNiCu-7 · AWS A5.11 ENiCu-7 | — | AMS 4574 |
Listed in NACE MR0175 / ISO 15156 for sour service; QQ-N-281. ASME pressure-vessel service to ~480 °C. UNS N04400.
| Alloy | Ni % | Key Element | Type | Best Used For |
|---|---|---|---|---|
| Alloy 400 | 63–70 | Cu 28–34 | Solid-solution Ni-Cu | Seawater, HF, reducing acids |
| Alloy K-500 | 63–70 | Cu 27–33 | Age-hardened Ni-Cu (Al+Ti) | Higher strength; pumps/shafts |
| Alloy 200 | ≥99.0 | — | Commercially pure Ni | Caustic/alkali; conductivity |
| Alloy 600 | ≥72 | Cr 14–17 | Ni-Cr-Fe | High-temperature oxidation |
| CuNi 70/30 | 30 (Ni) | Cu balance | Copper-base Cu-Ni | Seawater (lower strength/cost) |




