Copper Nickel Alloy 70/30 – UNS C71500 – Cupronickel

Topics Covered

Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Other Designations
Fabrication and Heat Treatment
    Annealing
    Cold Working
    Hot Working
    Welding
    Forging
    Machinability
Applications

Introduction

Copper-nickel alloys comprise 2 to 30% nickel and have high oxidation resistance and stress corrosion cracking resistance. Their high oxidation resistance is seen in moist air and steam. These alloys are thermally stable and possess moderate strength even when the temperature is high. The corrosion resistance and strength of these alloys are improved by the addition of manganese, iron, niobium, and or chromium. Copper nickel alloys also have good fabricability and high inherent resistance to biofouling.

The soluble nature of nickel in copper provides the copper nickel alloys with single phase alpha structures. The alpha dendrites in the cast structures contain a large amount of nickel starting from the center up to the edge of the dendrite. A large quantity of nickel is also present in interdendritic regions. The dendrite structure is broken by mechanical treatments. The alloying elements do not get homogenized even by repeated thermal and mechanical treatments.

Copper nickel alloys are of two types that include 70/30 and 90/10. The 70/30 copper nickel alloys have great resistance to sea water-related corrosion due to the presence of significant amounts of manganese and iron.

Copper nickel alloys are used in the following areas:

  • Desalination units
  • Hydraulic lines
  • Fish cages for aquaculture
  • Heat exchangers and condensers
  • Sea water pipework
  • Offshore fire water systems
  • Tubes for power plants and ships
  • Pumps, valves, sheathing and fittings for ship hulls

Chemical Composition

The chemical composition of UNS C71500 copper nickel alloys is outlined in the following table.

Element Content (%)
Copper, Cu 70.0
Nickel, Ni 30.0

Physical Properties

The following table shows the physical properties of UNS C71500 copper nickel alloys.

Properties Metric Imperial
Density 8.94 g/cm3 0.323 lb/in3
Melting point 2140°F 1171°C

Mechanical Properties

The mechanical properties of UNS C71500 copper nickel alloys are displayed in the following table.

Properties Metric Imperial
Tensile strength, ultimate 372-517 MPa 54000-75000 psi
Tensile strength, yield (depending on temper) 88.0-483 MPa 12800-70100 psi
Elongation at break (in 381 mm) 45.0% 45.0%
Charpy impact 107 J 78.9 ft-lb
Machinability (UNS C36000 (free-cutting brass) = 100%) 20% 20%
Shear modulus 57.0 GPa 8270 ksi
Poisson's ratio 0.34 0.34
Elastic modulus 150 GPa 21800 ksi

Other Designations

Equivalent materials to UNS C71500 copper nickel alloys are:

ASME SB111 ASME SB171 ASME SB359 ASME SB395
ASME SB466 ASME SB467 ASME SB543 ASTM B111
ASTM B122 ASTM B151 ASTM B171 ASTM B359
ASTM B395 ASTM B432 ASTM B466 ASTM B543
ASTM B552 ASTM B552 ASTM B608 ASTM F467
ASTM F468 DIN 2.0882 MIL C-15726 MIL T-15005
MIL T-16420 MIL T-22214 SAE J461 SAE J463

Fabrication and Heat Treatment

Annealing

UNS C71500 copper nickel alloys are annealed at temperatures between 649 and 816°C (1200 and 1500°F)

Cold Working

UNS C71500 copper nickel alloys have good cold working capacity.

Hot Working

Copper nickel 70/30 alloys are hot formed in an excellent manner.

Welding

Copper nickel 70/30 alloys can be welded using gas shielded arc welding, spot welding, coated metal arc welding, butt welding, seam welding, brazing, soldering and oxyacetylene welding processes.

Forging

Temperatures between 927 and 1038°C (1700 and 1900°F) are suitable for the 70/30 copper nickel alloys.

Machinability

The machinability rating of copper nickel 70/30 alloys is 20%.

Applications

UNS C71500 copper nickel alloys are used in areas where stainless steel cannot be used due to chloride stress-corrosion cracking and in other parts requiring high corrosion resistance. These alloys are also used as machined and forged valve and pump parts that are utilized for seawater services.


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