Nickel silver contains no silver whatsoever. The name is purely descriptive — these are
copper-nickel-zinc alloys, and the nickel bleaches the natural red of copper to a silver-white that closely resembles sterling. They are also sold as
German silver,
alpaca,
maillechort and
nickel brass, and the historical trade abbreviation
EPNS — electroplated nickel silver — refers to cutlery made by silver-plating a nickel silver base, where the base metal's own colour means a worn plating does not reveal an obviously different metal underneath. That single property, a silver appearance at a fraction of the cost, is the commercial foundation of the whole family.
Colour tracks the nickel-to-copper ratio, and so does price. At the bottom of the range
C74500 with 10% nickel retains a distinctly warm, pale-yellow cast. By
C75200 at 18% nickel the alloy reads as convincingly silver-white, which is why that grade is the classic.
C77000 holds the same 18% nickel against only 55% copper, giving both the whitest colour and the highest strength in the family. If appearance is a specified requirement, state the grade — the difference between 10% and 18% nickel is plainly visible side by side.
A note on the lead. The lead that makes this grade free machining also restricts where it can be used. Lead content is regulated in drinking-water contact components in most jurisdictions — in the United States under the Safe Drinking Water Act as amended, and in Europe under the Drinking Water Directive and associated national acceptance schemes — and in electrical and electronic equipment under RoHS, which grants copper-alloy exemptions that have been progressively narrowed. Lead also rules out most welding processes. Confirm the regulatory position for your market and application before committing a design to a leaded nickel silver; where lead is unacceptable, the unleaded grades are available at the cost of a much lower machinability rating.
These alloys contain 17–27% zinc, and that changes the corrosion rules completely compared with the copper-nickels. It is worth being blunt about this, because the C7xxxx UNS numbering invites the assumption that nickel silvers behave like
C70600 and
C71500. They do not.
Dezincification applies. In the copper-nickels there is no zinc to lose; here there is a great deal, and in stagnant or slightly acidic chloride waters the zinc can be selectively leached out, leaving a porous, mechanically worthless copper residue that retains the original shape. The nickel content improves resistance substantially over plain brass, but it does not eliminate the mechanism.
Ammonia stress-corrosion cracking — the classic ‘season cracking’ of brass — also applies, and a cold-worked or tightened nickel silver component carrying residual tensile stress will crack in moist ammonia, ammonium compounds, amines or nitrites. A
stress-relief anneal after cold work is genuinely important on these alloys, not a refinement.
Nickel silvers are not seawater alloys. They carry none of the deliberate iron addition that builds the protective film in the marine copper-nickels, and they should not be specified for seawater piping, condenser tube or any flowing-seawater duty. Their corrosion credentials are for atmospheric exposure, indoor and decorative service, food contact and freshwater — duties in which they perform well and tarnish slowly.
Every grade in this family is rated Poor for hot forming, and that is the governing manufacturing fact. Nickel silvers are hot-short: the zinc volatilises and the alloys crack rather than flow at forging temperature. They are therefore
cold-worked materials, and CDA rate most of them
Excellent for cold working to match. Components are blanked, drawn, spun, stamped, cold headed, swaged and roll-threaded from strip, rod or wire, with interstage annealing where the work is severe, and the final temper set by the last cold reduction. Annealing is carried out in the region of 538–816 °C depending on grade. Hot forging, hot extrusion and hot rolling are not practical routes for these alloys — design the part for cold forming from the outset.
How the eight divide. Six are unleaded and two are leaded free-machining grades. Among the unleaded, the key variable is the nickel-to-copper ratio, which sets both colour and strength.
C74500 (65-10) has the least nickel and the warmest colour;
C75700 (65-12) and
C75400 (65-15) step up through the middle;
C75200 (65-18) is the classic German silver and the industry reference.
C73500 is the high-copper, low-zinc member at 72% copper, giving the best corrosion resistance of the group and the standard coinage composition.
C77000 (55-18) holds the same 18% nickel at much lower copper, producing the whitest colour and much the highest strength — up to 1000 MPa as hard-drawn wire — which makes it the spring and contact grade. The leaded pair,
C78200 and
C79200, trade weldability for free-machining behaviour and are chosen for turned and screw-machined parts.
