Technical guide · 2026-08-14
Nickel-Copper Alloys
Nickel-copper alloys such as Alloy 400 combine resistance to seawater, nonoxidizing salts and selected alkaline or reducing environments with useful toughness, while precipitation-hardened K-500 adds strength at different fabrication risk.
01
Definition and boundary
This family is selected around marine and reducing service; it does not provide the chromium-based oxidation resistance of Ni-Cr alloys or the broad acid range of Ni-Cr-Mo systems.
Reference information only: final acceptance is controlled by the ordered product specification, condition, dimensions and certified test results.
02
How the material system works
Copper extends resistance in seawater and reducing media.
A single-phase solid solution supports toughness across temperature.
Aluminum-titanium precipitation strengthens K-500 after aging.
03
Representative grades and systems
| Grade or system | Selection focus | Qualification |
|---|---|---|
| Alloy 400 / UNS N04400 | General nickel-copper corrosion-resistant alloy. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| Alloy K-500 / UNS N05500 | Age-hardenable high-strength nickel-copper alloy. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| Alloy 405 / UNS N04405 | Free-machining variant whose sulfur addition affects welding. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
04
Properties and trade-offs
Seawater and brine resistance
Toughness including low temperature
Strength increase through age hardening in K-500
05
Product forms and supply conditions
06
Applications and selection
Applications and selection
- Marine shafts and fasteners
- Hydrocarbon and alkali equipment
- Valves, pumps and seawater tubing
Properties and trade-offs
- Check stagnant seawater and galvanic coupling.
- Select K-500 only when strength premium and heat treatment are justified.
- Avoid Alloy 405 where weldability is a primary requirement.
07
Fabrication, durability and inspection
Use controlled heat input and qualified filler selection.
Machine with rigid setups because work hardening is significant.
Verify K-500 age treatment and avoid hydrogen-assisted cracking conditions.
08
Procurement checklist
- State alloy/UNS and product standard.
- For K-500 define age condition and mechanical-property location.
- Specify PMI, NDT, surface condition and galvanic design assumptions.
09
Standards, sources and review
Standards and designation context
- UNS designation plus exact ASTM B-series product specification
- Applicable ASME construction code
- Qualified welding and heat-treatment procedure
Authoritative research sources
Nickel Institute · Technical overview, accessed 2026
Nickel Institute · Technical Guide 11012, revised edition
Nickel Institute · Technical Guide 393, 2021