What C44400 Antimony-Added Naval Brass Is
C44400 is a wrought copper-zinc-tin alloy of the admiralty brass family. Its copper content is held between 70.0% and 73.0% and its tin content between 0.9% and 1.2%, with antimony between 0.02% and 0.10% acting as the corrosion inhibitor and zinc forming the balance. The name naval brass is historic: the alloy is used in marine engineering, but its structure is single phase alpha, which places it alongside admiralty brass rather than alongside the duplex alpha-beta alloy C46400.
The practical value of the grade lies in the antimony addition. Selective leaching of zinc, known as dezincification, is the mechanism that destroys high-zinc brasses in slow-moving warm seawater. A very small, carefully controlled antimony addition changes the electrochemical behaviour of the surface just enough to suppress that mechanism, so the alloy can be used for thin-wall tubing and for components that see continuous seawater contact.
Chemical Composition and Standards
| Element | Weight % | Role |
|---|---|---|
| Copper (Cu) | 70.0-73.0 | Matrix; corrosion resistance and conductivity |
| Tin (Sn) | 0.9-1.2 | Solid solution strengthening; improves seawater resistance |
| Antimony (Sb) | 0.02-0.10 | Inhibitor against dezincification |
| Lead (Pb) | 0.07 max | Residual; strictly limited for hot workability |
| Iron (Fe) | 0.06 max | Residual; kept low to protect ductility |
| Zinc (Zn) | Balance | Principal alloying element |
Seamless heat exchanger and condenser tube in this grade is ordered to ASTM B111, which is mirrored in the ASME SB111 specification. The alloy belongs to the same inhibited brass group as the arsenic-modified C44300 and the phosphorus-modified C44500, and all three share the HSn70-1 type designation used in the Chinese system under GB/T 8890.
Mechanical Properties and Behaviour
| Property | Typical value |
|---|---|
| Tensile strength | 290-370 MPa, depending on temper and processing |
| Yield strength | 110-280 MPa |
| Elongation | 15-40% |
| Density | Approximately 8.5 g/cm³ |
| Structure | Single phase alpha, fully annealable |
The spread in strength and elongation reflects the difference between soft annealed tube, which is supplied for roller expanding and bending, and the light cold-worked conditions used for parts that must hold their shape under load. For pressure-containing tube the mechanical property requirements of ASTM B111 for the ordered temper should be quoted directly on the purchase order and confirmed on the mill test certificate, rather than relying on typical values.
Corrosion Resistance in Seawater
C44400 resists general seawater corrosion well and, because of the antimony addition, it also resists selective zinc loss far better than an uninhibited high-zinc brass. It performs best in flowing, reasonably clean water; deposits, silt, dead legs and stagnant pockets are the conditions that defeat every inhibitor system through under-deposit attack and local crevice corrosion.
Where erosion or impingement is a risk, tube velocity should be kept inside the design range appropriate to the alloy and the water chemistry. Where ammonia or amine compounds are present in the cooling water, brass alloys as a group become susceptible to stress corrosion cracking, so residual stress should be relieved and the water chemistry controlled.
Applications and Processing
Thermal desalination and water treatment. Heat exchanger tube, evaporator tube and condenser tube in multi-stage flash and multi-effect units, and in cooling water systems.
Pumps and valves. Bodies, impellers, stems and seats in seawater transfer, ballast and firefighting systems.
Piping and fittings. Flanges, couplings, elbows and pipework on shipboard and offshore platform systems.
Marine structures and deck hardware. Components exposed to spray and immersion where corrosion resistance and moderate strength are both required.
Instrumentation and electrical parts. Marine instrument housings, terminals and contactors that must resist humid, salt-laden atmospheres.
Manufacturing normally follows casting, hot working and cold finishing. Hot working is carried out from roughly 700 C downward, with a final cold drawing or cold finishing pass to set dimensions and surface quality, followed by an anneal that removes internal stress. Lead is held to 0.07% or less because higher levels embrittle the alloy at hot working temperature, and that limit should be respected by the melt shop rather than pushed for machining convenience.
Selection and Inspection Notes
Match the inhibitor to the water chemistry. C44400, C44300 and C44500 differ principally in which element is used to block dezincification, so the choice should follow the cooling water analysis and the specification of the end user.
Verify the chemistry. Because the inhibitor works at only a few hundredths of a percent, the mill test certificate must record antimony by analysis rather than by nominal grade.
Confirm the temper. Soft tube for expanding, light cold work for structural parts; check tensile and hardness results against ASTM B111 for the ordered condition.
Apply non-destructive testing for tube. Eddy current testing is standard practice for condenser tube, and hydrostatic testing is added where pressure integrity is critical.
Protect during storage. Cap tube ends, avoid contact with ammonia-bearing packaging or marking inks, and store under cover to prevent chloride staining.
FAQ
Q: Is C44400 an admiralty brass or a naval brass?
Metallurgically it belongs to the admiralty brass family: it is a single phase alpha copper-zinc-tin alloy with an inhibitor. The word naval in the trade name reflects the marine duty rather than the duplex alpha-beta structure of conventional naval brass.
Q: How does antimony protect the alloy?
The controlled addition raises the electrochemical potential of the alloy surface and interrupts the selective dissolution of zinc, which is the mechanism that causes dezincification in high-zinc brasses exposed to warm, slow-moving seawater.
Q: What is the difference between C44300 and C44400?
Both are inhibited admiralty brasses of similar copper and tin content. C44300 uses arsenic as the inhibitor, while C44400 uses antimony; the choice is usually dictated by the end user specification and by water chemistry rather than by mechanical properties.
Q: Can C44400 be welded?
Brazing and soldering are the preferred joining methods. Fusion welding is possible but demands matching filler, low heat input and good gas shielding, because the same elements that inhibit corrosion also affect weld pool fluidity.
Q: Which forms are normally available?
Seamless tube and pipe, rod and bar, plate and sheet, strip and wire. Tube is the dominant form because the alloy is most often used for heat transfer surfaces.
Q: What should be specified on a purchase order?
The UNS number, the governing standard such as ASTM B111 for tube, the temper, dimensions with tolerances, the test requirements including eddy current or hydrostatic testing, and the documentation required for shipment.
