Copper-Nickel Alloys - Marine Supreme: Types of Copper-Nickel Alloy

Copper Applications in Metallurgy of Copper & Copper Alloys

By Vin Callcut

The copper-nickel alloys are single-phased throughout the full range of compositions and many standard alloys exist within this range, usually with small additions of other elements for special purposes. The first of these special uses for copper-nickels was as marine condenser tubes. There are now many others, described later. Other copper-nickel alloys are used for coinage and wire mesh for the paper industry, but the two most popular alloys for marine applications are those that contain 10% or 30% nickel.

Manganese is invariably present in the commercial alloys as a deoxidant and desulfurizer; it improves working characteristics and additionally contributes to corrosion resistance in seawater. Other elements that may be present singly or in combination are:

Iron is added (up to about 2%) to alloys used in marine applications. It confers resistance to impingement attack by flowing seawater. The initial development of the optimum compositions of the copper-nickel-iron alloys took place in the 1930s. This work was undertaken to meet naval requirements for improved corrosion-resistant materials for tubes, condensers and other applications involving contact with seawater. Throughout this publication the term "copper-nickel" refers in fact to copper-nickel-iron alloys.

Chromium can be used to replace some of the iron content and at one percent or more provides higher strength. It is used in a 30% nickel casting alloy (IN-768).¹ A low-chromium 16% nickel wrought alloy (C72200)² has been developed in the USA.

Niobium (Columbium) can be used as a hardening element in cast versions of both the 10% and 30% nickel alloys (in place of chromium). It also improves weldability of the cast alloys.

Silicon improves the casting characteristics of the copper-nickel alloys and is used in conjunction with either chromium or niobium.

Tin confers an improved resistance to atmospheric tarnishing and at the 2% level is used with 9% nickel to produce the alloy C72500. This alloy has useful spring properties and is used in the electronics industry. It is not often recommended for marine applications.

Impurities

Impurity elements such as lead, sulfur, carbon, phosphorus, etc., in the amounts to be found in commercial material, have little or no effect on corrosion performance, but because of their influence on hot ductility may impair weldability and hot workability and are, therefore, carefully controlled.

Variations in the common national and international specifications for the 90/10 and 70/30 alloys are shown in Table 2. From this, the extent to which various standard materials overlap may be compared. In some standards the impurities are more closely controlled than others but in all cases the material supplied will be fit for its designated purpose. However, the limits for some impurities (such as lead) in the specifications do not guarantee weldability by all techniques. In cases of doubt, the supplier's advice should be obtained.

**Table 2**.Standard Compositions of Wrought Copper-Nickel Alloys, North American and European Designations
American Designations	Composition, % (Range or Max)
UNS Alloy No.	Cu	Pb	Fe	Zn	Ni (incl Co)	Sn	Mn	Others*
C70600	Rem	0.05	1.0-1.8	1.0	9.0-11.0		1.0
C71500	Rem	0.05	0.4-1.0	1.0	29.0-33.0		1.0
C71640	Rem	0.01	1.7-2.3		29.0-32.0		1.5-2.5	0.03S 0.06C
*Special limits apply when the product is to be welded.

Symbol	Number	Cu	C	Co*	Fe	Mn	Ni	P	Pb	S	Sn	Zn	Others
European Designation		Composition, % (Range or Max)
CuNi10-Fe1Mn	CW352H	Rem	0.05	0.1	1.0-2.0	0.5-1.0	9.0-10.0	0.02	0.02	0.05	0.03	0.05	0.2
CuNi30- Fe2Mn2	CW353H	Rem	0.05	0.1	1.5-2.5	1.5-2.5	29.0-32.0	0.02	0.02	0.05	0.05	0.5	0.2
CuNi30-Mn1Fe	CW354H	Rem	0.05	0.1	0.4-1.0	0.5-1.5	30.0-32.0	0.02	0.02	0.05	0.05	0.5	0.2
*Co max 0.1% is counted as Ni.

The forms in which the various standard compositions are available are shown in Table 3. Future references in this publication to 90/10 and 70/30 copper-nickel alloys refer to the alloys normally containing iron and manganese as used in marine applications. When the 70/30 alloy is mentioned, it normally contains less than 1% each of iron and manganese but in some circumstances, it is preferable to use material with about 2% iron and 2% manganese rather than the alloy with lower iron and manganese. (See Todd.)

Table 3 shows the common production limits on the sizes of these materials. This is a guide to what is commonly made to order. It may also be possible to make material outside these sizes by arrangement with the supplier. Provided foundry practice is good, satisfactory complex castings can be made in the copper-nickels. The 90/10 composition has a lower melting and pouring temperature than the 70/30 alloy. Normally, for small castings, additions of some extra alloying elements are made to improve properties.

**Table 3**.Standard Compositions of Wrought Copper-Nickel Alloys, North American and European Designations
Form	Sizes
Form	Metric	English
Plate	up to 3000 mm wide, 10 to 150 mm thick	up to 10ft wide, ¼-6 in. thick
Clad steel plate	to order only	To order only
Sheet & Strip	up to 2000 mm wide, 0.2-10 mm thick	up to 6ft wide, 0.008-0.25 in. thick
Seamless Tubes: Pipeline	8-420 mm OD 0.8-5.0 mm wall thickness	0.3-16 in mm OD, 0.03-0.2 in wall thickness
Condenser	8-35 mm OD 0.75-2.0 mm wall thickness	0.3-1.5 in OD, 0.03-0.1 in wall thickness
Coiled	6-22 mm OD 0.5-3 mm wall thickness	0.25-1 in OD, 0.02-0.12 in wall thickness
Tubes - longitudinally welded	270-1600 mm OD 2.0-10 mm wall thickness	10-63 in OD, 0.1-0.5 in wall thickness
Fabrications	by arrangement	by arrangement
Wire	all common wire and wire mesh sizes	all common wire and wire mesh sizes
Rod & Section	all common sections up-180 mm diameter	all common sections up-7 in diameter
Welding Consumables	all common sizes	all common sizes
Note: The sizes listed below represent typical manufacturing capabilities. They are not necessarily available from stock, nor in every alloy. Larger sizes may be available to special order.

The introduction of electric furnace melting in foundries has led to a greater interest in 70/30 alloys, in particular an alloy containing 1.5-2.5% chromium, which has exceptional resistance to impingement corrosion, making it ideal for heavy duty marine pump and piping applications. An alternative 70/30 alloy, also specified for naval use, contains 0.5-1.5% niobium and other closely specified elements. Since these alloys have tight limits on impurities, only certified ingots are used. Electric melting practice is essential for these alloys, since it attains the correct melting temperature in reasonable time and provides a cleaner furnace atmosphere, thus avoiding contamination and gas pick-up. The modified alloys are therefore only available from foundries equipped with electric arc furnaces.

For security and other reasons, the copper-nickel alloys used for a large percentage of the world's coinage requirements do not necessarily conform to any of the common specifications cited here. Generally, the coinage alloys do not include iron, manganese or other elements present in industrial alloys. The outer layers of the U.S. Susan B. Anthony dollar, for example, are made from an alloy containing 12.5% nickel and 87.5% copper. The outer layers of the quarter, dime and 50-cent piece are 75% copper-25% nickel. The cores of these "sandwich" coins are pure copper. The nickel 5-cent coin is made from 75% copper-25% nickel throughout. Since coinage alloys constitute a very specialized application, they are not considered in this publication.

Typical mechanical properties for the 90/10 and 70/30 alloys are given in Table4 and Table5. Further data are included in Copper Nickel 90/10 and 70/30 Alloys - Technical Data (CDA-UK Publication No 31 PDF 643KB). Material should normally be ordered to the appropriate minimum properties quoted in the standard specification used.

**Table 4**. Mechanical Properties of 90/10 Copper-Nickel-Iron Alloy
Form	Condition	0.1 % proof stress		Tensile strength		Elongation on 5.65 So	Hardness	Shear strength
Form	Condition	N/mm²	KSI	N/- mm²	KSI	%	HV10	N/mm²	KSI
Tube	Annealed Cold drawn (hard) Temper annealed	140 460 190-320	18 60 24-42	320 540 360-430	42 70 46-56	40 13 38-30	85 165 115-140	250 360 280-320	32 46 36-42
Plate	Annealed Hot rolled	120 140-190	18-24	320 340-360	42 44-46	42 40	85 95-105	250 260	32 34
Sheet	Annealed Hot rolled Cold rolled	120 180 380	16 24 50	320 360 420	42 46 54	42 40 12	85 105 125	250 260 290	32 34 38
Note: Typical values and ranges are listed. Exact values vary with composition, size and heat treatment.

**Table 5**. Mechanical Properties of 70/30 Copper-Nickel-Iron Alloy
Form	Condition	N/mm²	KSI	N/mm²	KSI	%	HV10	N/mm²	KSI
Form	Condition	0.1 % proof stress		Tensile strength		Elonga- tion on 5.65 So	Hard- ness	Shear strength
Tube	Annealed Cold drawn (hard) Temper annealed	170 370-570 200-340	22 48-74 26-44	420 510-660 430-490	54 66-86 56-64	42 20-73 5-25	105 105-190 120-140	310 320-370 320-370	40 42-48 42-48
Plate	Annealed Hot rolled	150 170-200	20 22-26	390 400-430	50 52-56	42 40	95 105-120	290 310-320	38 40-42
Sheet	Annealed Hot rolled Cold rolled	150 200 430	20 26 56	390 430 500	50 56 64	42 40 16	95 120 140	290 320 350	38 42 46
Note: Typical values and ranges are listed. Exact values vary with composition, size and heat treatment.

References:

1. INCO Designation

2. UNS designation. A description of copper alloys listed under the UNS numbering system can be found in the Resources section

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