UNS C70600, globally recognized as Cupro-Nickel 90/10 or Alloy 706, is a premier marine-grade copper alloy engineered specifically for relentless exposure to flowing seawater. Comprising approximately 90% Copper and 10% Nickel, this alloy is distinctively fortified with a crucial ~1.4% addition of Iron (Fe). This specific iron inclusion profoundly alters the alloy's surface chemistry, forming a highly tenacious, self-repairing protective oxide layer that shields the metal from high-velocity seawater erosion and impingement attacks.
Beyond its structural stability and excellent fabrication qualities, C70600 possesses inherent biocidal properties. The copper-rich matrix actively repels marine biofouling, preventing the attachment of barnacles, algae, and mollusks. This combination of anti-fouling capabilities, absolute immunity to chloride stress-corrosion cracking, and total lack of magnetic permeability makes Cupro-Nickel 90/10 fasteners the cornerstone of naval shipbuilding, offshore desalination piping, and coastal power generation cooling loops.
| Material Classification | Copper-Nickel Alloy (90/10 CuNi) |
|---|---|
| UNS Designation | C70600 |
| Microstructure | Single-Phase Alpha Solid Solution |
| Magnetic State | Completely Non-Magnetic |
| Density | 8.94 g/cm³ (0.323 lb/in³) |
| Size Range | Metric: M4 to M48 | Imperial: 3/16" to 2" |
| Primary Attribute | Supreme Resistance to Marine Biofouling & Seawater Erosion |
Contains detailed maximum seawater velocity limits, galvanic compatibility charts for mating with Titanium or Super Duplex piping, and approved maritime welding parameters for C70600 studs.
⬇ DOWNLOAD DATASHEETIn high-stakes naval and offshore engineering, the precise balance of Iron and Nickel is critical. If the Iron content drops below 1.0%, the alloy's resistance to seawater erosion plummets. Ananka provides absolute metallurgical transparency mapping back to the primary mill.
The formulation of C70600 is elegantly specialized for the ocean. Nickel provides general structural stability and prevents pitting, while the specific inclusion of Iron (Fe) combined with trace Manganese (Mn) generates the impenetrable, self-healing oxide film necessary to survive fast-moving, turbulent seawater.
| Copper (Cu) | Nickel (Ni) | Iron (Fe) | Manganese (Mn) | Zinc (Zn) | Lead (Pb) |
|---|---|---|---|---|---|
| Balance (~88.6) | 9.0 – 11.0 | 1.0 – 1.8 | 1.0 Max | 1.0 Max | 0.05 Max |
| Mechanical Property | Typical Limits (Half-Hard Temper) |
|---|---|
| Tensile Strength | 44,000 - 60,000 psi (300 - 415 MPa) |
| Yield Strength | 20,000 - 45,000 psi (140 - 310 MPa) |
| Elongation (in 2 inches) | 25% - 40% |
| Hardness (Rockwell B) | 65 - 80 HRB |
| Standard / System | Designation |
|---|---|
| ASTM Specifications | ASTM B151 (Rod & Bar), ASTM F467 / F468 |
| Common Trade Names | 90/10 CuNi, Alloy 706, Copper-Nickel 10% |
| European Equivalent | EN CW352H / CuNi10Fe1Mn (DIN 2.0872) |
| Military / Marine Std | MIL-C-15726 (US Navy), DEF STAN 02-779 (UK) |
| Mating Bolts/Studs | Internal Threads (Nuts) | Washers |
|---|---|---|
| C70600 CuNi Hex Bolts & Studs | C70600 Finished Hex Nuts | C70600 CuNi Flat Washers |
C70600 is highly ductile and features a relatively low yield strength compared to alloy steels or Aluminum Bronzes. Overtorquing will rapidly stretch the bolt beyond its elastic limit. Thread galling is also a persistent risk in marine environments; premium marine-grade, nickel-compatible anti-seize must be utilized during joint assembly.
| Nominal Diameter | Threads Per Inch (UNC) | Max Target Torque (in-lbs) | Max Target Torque (ft-lbs) |
|---|---|---|---|
| 1/4" | 20 | 60 - 70 | ~ 5.5 |
| 3/8" | 16 | 180 - 200 | ~ 16 |
| 1/2" | 13 | 360 - 400 | ~ 32 |
| 3/4" | 10 | 1200 - 1400 | ~ 110 |
Pure Copper-Nickel is excellent at resisting stagnant saltwater, but when seawater flows rapidly through a pipe or around a bolt, the sheer mechanical force of the water tears the protective oxide layer away, leading to rapid "impingement" erosion. The addition of just 1.0% to 1.8% Iron radically strengthens that oxide layer, allowing the metal to withstand much higher water velocities without eroding.
C71500 (70/30) contains 30% Nickel, making it significantly stronger and capable of withstanding even higher seawater velocities than the 90/10 grade. However, 70/30 is considerably more expensive and harder to machine. For the vast majority of general marine piping, cooling loops, and submerged hull hardware, 90/10 (C70600) provides the optimal, cost-effective balance of corrosion resistance and biocidal performance.
Yes. The high copper content in C70600 naturally releases microscopic copper ions into the immediate surrounding water. This local environment is highly toxic to marine microorganisms, larvae, and biofouling agents like barnacles or mussels. Using CuNi fasteners on underwater grates or pump housings ensures those components remain clear of marine growth, eliminating the need for constant mechanical scraping.
