June 2000

Copper-Nickel Alloys - Marine Supreme: Fabrication

Copper Applications in Metallurgy of Copper & Copper Alloys

By Vin Callcut

Hot and cold working techniques may be used for the forming of wrought materials to required shapes though cold working is normally be to preferred. For the 90/10 alloy the hot working temperature range is from 1,652ºF (900ºC) down to about 1,472ºF (800ºC) while for the 70/30 material it is from 1,742ºF (1950ºC) down to about 1,562ºF (850ºC). If substantial working is required, it is always useful to consult the supplier for recommendations.

The maximum amount of cold work possible before an anneal is required may be al large as 50&percent; dependent on the material form and deformation process used. Tubes may be bent by the usual methods with care being taken to produce smooth bends to assist non-turbulent liquid flow in service.

Stress corrosion is not a problem normally encountered with copper-nickel alloys but if after excessive cold work a stress relief heat treatment is required, a temperature of 572 - 752ºF (300 - 400ºC) will suffice. For full annealing 1,292 - 1,472ºF (700 - 800ºC) is needed for the 90/10 alloy and 1,382 - 1,562ºF (750 - 850ºC) for the 70/30 alloy with time and temperature dependent on the extent of cold work in the alloy, the section thickness and annealed temper and grain size required. Oily residues must be removed before annealing in order to prevent the possible formation of carbonaceous films which can lead to pitting corrosion and can enhance susceptibility to impingement attack in some service conditions, as is also the case with copper and other copper alloys. Most producers of the alloys are able to advise on their fabrication and use.

See the list of references for descriptions of joining by welding and brazing of these materials.

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