CAL Wrought CNC versus NAB and cast CNC

High Strength Wrought Copper-Nickel-Chrome Alloy CuNi30Cr1MnFeSiZrTi – composition compliant with generic alloy Def Stan 02-886, with enhanced strength and toughness exceeding specification requirements.

In our copper nickel chrome alloy (CuNi30Cr1MnFeSiZrTi), high strength is combined with extremely high toughness and good ductility together with outstanding seawater corrosion resistance.

Background

This outstanding material (Copper-Nickel-Chrome alloy/CNC) was developed by the British MoD to replace nickel aluminium bronze (NAB) in seawater systems on submarines, due to corrosion issues with NAB, in particular selective phase corrosion (SPC). The depth of attack in NAB is typically 1.1mm/year (0.043″/year), but has been observed at 1.4mm/year (0.055″/year). CNC is reported to have the ability to last the lifetime of the platform and observed 10 years service performance showing excellent results with negligible corrosion and fit for a second commission.

CNC does not contain continuous/semi-continuous anodic phases and as such, is immune to SPC and has a very low general corrosion rate.

The resulting specification – Def Stan 02-824 part 1 – is for castings and due to extreme difficulties in producing sound castings – in particular avoiding metal oxide films which form during melting and casting – its cost is generally high and its usage limited. For these reasons, it has not generally replaced NAB in seawater systems in submarines.

During the development of the cast version of the alloy, a number of companies were sponsored to develop a wrought (forged) version, but this was abandoned due to reported lack of forgeability.

Our advanced melting, alloying and casting techniques, combined with a deep metallurgical understanding of hot working materials, have allowed us to develop two forged versions of the alloy, which is very exciting. There is a ‘standard’ version (CNC-1) and a higher strength version (CNC-2) applicable to bars to around 150mm (6″) in section.

If you are using NAB in critical seawater systems where resistance to corrosion and high shock resistance is required, you need to change to this material!

Mechanical Properties CAL CNC-1 & CNC-2

  • High Strength Cupper-Nickel-Chrome Alloy
  • CuNi30Cr1MnFeSiZrTi

Table 2 – Guaranteed Minimum Mechanical Properties*

Product → Bars – Round, square, flats, hexagon, shapes Forgings Cast CNC Def Stan 02-824 part 1 for reference
Material section-size (minor dimension)
Property ↓ Up to and including 150mm (6″) Over 150mm (6″) All sizes
CNC-1 CNC-2* CNC-1 CNC-1
Ultimate Tensile Strength Rm MPa 580
(84Ksi)
680
(99Ksi)
550
(80Ksi)
550
(80Ksi)
480
(70Ksi)
0.2% Proof Stress Rp0.2 MPa 390
(57Ksi)
600
(87Ksi)
350
(51Ksi)
350
(51Ksi)
300
(44Ksi)240 (35Ksi)
for design
% Elongation after Fracture 5.65 √ So 20 14 20 20 18
Izod Impact J 110
(81ft lbf)
90
(66ft lbf)
110
(81ft lbf)
110
(81ft lbf)
Typical 45-60
(33-44ft lbf)
Hardness Brinell HB 10/3000** 160-200 190-225 160-200 160-200 Typical 170-200

*Available as ‘long products’ (bars and rods) to around 150mm in section
** For reference only – does not form part of the acceptance criteria unless agreed

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Corrosion Data

Wrought CuNiCr is specifically designed for applications where a combination of high shock resistance (resistance to crack propagation under dynamic loading) combined with high resistance to sea water corrosion is required. In particular, it offers benefits for critical components in equipment used in military submarines and fighting ships, where longevity and functionality are crucial over the life of the platform.

The structure of the alloy is free from vulnerable phases and as such is immune to selective phase corrosion (SPC), unlike Nickel Aluminium Bronze. Corrosion is only slight and general (on the metal surface) with no sub-surface attack, making the material fit for wetted sealing-faces. Being a copper based alloy, the material’s resistance to marine bio-fouling is high and similar to conventional copper-nickel alloys, such as 90/10 and 70/30 Cupro Nickel. Surfaces therefore remain ‘clean’, avoiding accelerated corrosion and reduced functionality associated with marine growth.

The electrochemical potential of wrought CuNiCr is similar and compatible with the other copper alloys used in seawater systems, for example 90/10 and 70/30 CuNi alloys and Nickel Aluminium Bronze and are interchangeable within systems.

View corrosion data

Physical Properties

Table 4 – Physical Properties

Properties Metric Imperial
Melting point 1,180-1,230°C 2,156-2,246°F
Density 8,800 kg/m³ 0.318 lbs/in³
Thermal Conductivity @ 20°C 23 W/(m.°K) 13.3 Btu/(Hour.Ft.°F)
Electrical Resistivity at 20°C 0.35 μ.Ω.m 13.8 μ.Ω.in
Electrical Conductivity %IACS at 20°C 5 5
Coefficient of linear expansion (0-250°C) 18.0 x 10-6/°C 10.0 x 10-6/°F
Specific Heat 0.411 J/(g.°K) 0.0982 Btu/(lb.°F)
Magnetic Permeability (μr) 1.01
0.2% Proof Stress 300-320Mpa
Tensile Strength 480-540Mpa
Elongation, % on gauge length = 5.65√S0 18-25
Reduction of area 30-50%
Shear Strength 240-270 N/mm² 34.8 ksi
Brinell Hardness 170-200
Young’s Modulus, Modulus of Elasticity 143,000 N/mm² 20,740 ksi
Modulus of Rigidity 54,000 N/mm² 7,832 ksi
Poisson’s Ratio 0.3 0.3
Izod impact value 110J
Corrosion potential in seawater -0.18Vsce
General corrosion rate 0.02mm/year
Crevice corrosion rate <0.02mm/year
Selective Phase Corrosion rate 0mm/year
Impingement resistance 6-8m/s

Additional information can be provided upon request

Applications

This combination of properties is unique and consequently is unavailable elsewhere in a copper based alloy.

Wrought CNC is specifically designed for applications where a combination of high shock resistance (resistance to crack propagation under dynamic loading) combined with high resistance to sea-water corrosion is required. In particular, it offers benefits for critical components in equipment used in military submarines and fighting ships, where longevity and functionality are crucial over the life of the platform.

Current components being manufactured in nickel aluminium bronze can be replaced by CAL Wrought CNC-1 / CNC-2 generally without the need to change geometry, however this will lead to an increase in component weight of around 15% due to the increase in density. If however full use is made of the following benefits, a decrease in component weight can be realised with obvious benefits including reduced inertia under shock conditions:

  • Increased 0.2% proof stress over NAB
  • Massively increased resistance to shock of NAB
  • Much higher sea-water corrosion resistance. In particular very low crevice corrosion and lack of selective phase corrosion i.e. reduction in in-service corrosion allowance

Like conventional cupro-nickel alloys, CuNiCr can suffer from galling. When excellent anti-galling characteristics are required, extreme-strength cupro-nickel CAL T-1000 CuAl14Al2 is recommended.

Typical applications include sea-water retaining covers, clamps, flanges, valve bodies and internal components, seal-rings, actuators, heat exchangers. The higher strength version CNC-2 is ideal for fasteners.

Inspection and Certification

  • High Strength Wrought Copper-Nickel-Chrome Alloy
  • CuNi30Cr1MnFeSiZrTi

Table 5 – inspection and testing grades and classes

Product form
Bars Forgings
Grade / Class1
Grade 11 Class 11 Class 21
Chemical Analysis (melt) Every cast Every cast Every cast
Mechanical Testing2 Every cast for each size
Integral sample2
Each and every forging
Integral sample2
One forging every cast/size
Integral sample2
Ultrasonic Inspection 100% Def Stan 02-729 part 5 100% Def Stan 02-729 part 5 100% Def Stan 02-729 part 5
Dye Penetrant Inspection 100% Def Stan 02-729 part 43 100% Def Stan 02-729 part 4 100% Def Stan 02-729 part 4
Visual Inspection 100% 100% 100%
Eddy Current4 100% Def Stan 02-729 Part 34 100% Def Stan 02-729 Part 34 100% Def Stan 02-729 Part 34

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Forms Available

We can provide the largest and heaviest-section forged products available anywhere due to industry-leading large ingot sizes that ensure a large total forging reduction and a uniform fine-grain wrought structure in the finished product.

Our capacity continues to evolve and widen as we service ever-increasing customer demands.

  • Bars (square/flat/round) from 10mm to 500mm (0.375-20″) in section
  • Forgings (to 5 Tonnes): Blocks/Rings to 2400mm (95″) outer ø / Shafts to 7M long/Discs to 1250mm (49″) ø
  • Note: The higher strength version CAL Wrought CNC-2 is only available as bars to around 150mm (6″) in section.
  • Proof-machined or fully-machined components.

Composition

  • Complies with Def Stan 02-886 Table 1
  • High Strength Cupper-Nickel-Manganese-Aluminium Alloy
  • CuNi15Mn4Al1Fe

Table 1 – Composition requirements weight %

Alloying Elements
Cu Ni Cr Fe Mn Si Zr Ti
Remainder 29.0-32.0 1.6-2.0 0.5-1.0 0.5-1.0 0.20-0.40 0.05-0.15 0.03-0.15
Impurity Elements – ultra low levels (all figures are maximum)
Permitted Total of these Impurities 0.070% maximum by weight
Pb P Bi S C Co B
0.005 0.005 0.001 0.005 0.020 0.050 0.001

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Manufacture

Our expertise allows us to cast high quality ingots suitable for forging, using advanced melting, alloying and casting techniques. Additionally, our deep metallurgical understanding of forging and other hot working activities, allows us to create a range of high quality wrought products including forgings (rings, discs, blocks, shafts, closed die forgings) and bars (round, square, hexagonal, flats).

All material (CAL CNC-1 and CNC-2) is subjected to a stress relieving heat treatment after all working operations are complete, as required by Def-Stan 02-886. This heat treatment involves raising the temperature to 475°C ± 15°C (887°F) at a maximum rate of 200°pC/hour, then holding for 1 hour per 25mm (1″) of section (2 hours minimum) followed by cooling to ambient temperature in still air within the workshop environment.

Wrought CNC is available in two conditions:

  • CAL CNC-1: The standard material applicable to all product forms and sizes
  • CAL CNC-2: High strength version applicable to bars (round/flat/square/hexagonal) up to around 150mm (6″) in section.

Characteristics

  • Extremely high toughness ≈ 100J higher than NAB and double that of cast CuNICr
  • 0.2% proof stress twice that of Nickel Aluminium Bronze and significantly higher than cast CuNiCr, allowing designers to work on a minimum proof stress of 350-390 MPa (CNC-1) / 600MPa (CNC-2) rather than 240MPa for cast CuNiCr. (51-56Ksi (CNC-1) / 87Ksi (CNC-2) rather than 35Ksi for cast CuNiCr)
  • High mechanical strength and ductility
  • Extremely high shock resistance
  • Lack of selective phase corrosion (SPC)
  • Immune to hydrogen embrittlement and stress corrosion cracking in sea-water
  • No loss of properties at cryogenic temperatures
  • Good resistance to stress corrosion cracking in hydrogen sulphide conditions
  • Anti bio-fouling (lack of marine growth)
  • High resistance to impingement/erosion/cavitation/pitting in sea-water
  • Outstanding resistance to sea-water corrosion both general (self) and pitting corrosion
  • High modulus of elasticity compared with other copper-based alloys
  • Low relative magnetic permeability – virtually non-magnetic
  • Easily machined to a high surface finish and dimensionally stable
  • Non-sparking
  • Uniform fine grain structure permits volumetric inspection using ultrasonic techniques
  • Cost-effective compared with cast CNC and other materials e.g. Nickel Aluminium Bronze

Download CAL Wrought CNC Datasheet

Contact

+44 (0) 1782 816888

[email protected]

Auckland Street, Stoke-on-Trent, ST6 2AZ, United Kingdom