What Is Cartridge Brass 260?
Cartridge brass 260 is the traditional name for UNS C26000, a single-phase alpha brass containing roughly seventy per cent copper and thirty per cent zinc. The name comes from its long-established use in drawn cartridge cases, for which its combination of high ductility and useful strength is ideal. It remains the most heavily used of all the copper-zinc alloys because it can be cold formed to a high degree, then strengthened by the working itself without any heat treatment.
Because the alloy is a single-phase solid solution, it can be deep drawn, spun and stamped far more severely than the two-phase brasses, and it retains good fatigue resistance after forming. It is supplied as sheet, strip, plate, rod, bar, wire and tube, with the temper selected to match the intended forming operation.
Chemical Composition
| Element | Composition (% by weight) |
|---|---|
| Copper (Cu) | 68.5 - 71.5 |
| Zinc (Zn) | Remainder |
| Lead (Pb) | 0.07 max |
| Iron (Fe) | 0.05 max |
| Other elements, total | 0.15 max, within the limits of the product specification |
Copper content is deliberately held in the narrow 68.5 to 71.5 per cent band. Below it, a second phase begins to appear and cold formability falls sharply; above it, strength and machinability suffer. Lead and iron are kept at residual levels because they reduce ductility in severe drawing operations, and a low-lead composition also makes the grade easier to place in markets with restrictions on lead in plumbing applications.
Physical and Mechanical Properties
| Property | Typical value |
|---|---|
| Density | 8.53 g/cm³ |
| Melting range | About 915 - 955 C |
| Electrical conductivity | About 28 per cent IACS |
| Thermal conductivity | About 120 W/m.K at 20 C |
| Coefficient of thermal expansion | About 20 × 10-6 per K over the normal working range |
| Modulus of elasticity | About 110 GPa |
| Machinability rating | 30, with free-cutting brass taken as 100 |
| Temper | Tensile strength | Yield strength (0.5 % ext.) | Elongation | Hardness |
|---|---|---|---|---|
| Annealed (O) | 300 - 400 MPa | 100 - 150 MPa | 55 - 70 % | 50 - 70 HV |
| Half hard (H02) | 450 - 550 MPa | 350 - 420 MPa | 15 - 25 % | 100 - 130 HV |
| Hard (H04) | 550 - 650 MPa | 480 - 550 MPa | 5 - 12 % | 140 - 180 HV |
The dramatic difference between the annealed and hard tempers illustrates the alloy's principal characteristic: strength is generated by cold work rather than by alloying or heat treatment, and temper must therefore be specified precisely for each part.
Fabrication and Joining Behaviour
Cold forming. Excellent. Deep drawing, stamping, coining, spinning and bending are all routine, which is the reason for the alloy's association with cartridge cases and drawn shells.
Machining. Moderate. Without intentional lead additions the chips are stringy, so sharp tooling, positive rake and adequate lubrication are needed to control chip formation and surface finish.
Soldering and brazing. Excellent for both soft soldering and brazing, with no notable difficulty in producing sound joints.
Welding. Oxyacetylene and gas-shielded arc welding are possible but the zinc content makes fume control necessary, and shielded metal arc welding is not recommended because the flux residues and dilution make the joint unreliable.
Hot forming. Fair. The alloy is normally processed cold and annealed as required rather than hot worked.
Interstage annealing is the usual accompaniment to severe cold reduction. Typical practice is a recrystallisation anneal in the range of about 425 to 600 C in a controlled atmosphere, followed by cooling before the next drawing or forming operation.
Corrosion Resistance and Service Limits
Cartridge brass performs well in rural, urban and marine atmospheres, in fresh water and in many neutral aqueous solutions, and it is widely used outdoors for decorative and structural hardware. The limitations matter just as much as the strengths. The alloy is not suitable for contact with acetic acid, moist ammonia or ammonium compounds, hydrochloric acid or nitric acid, and it is attacked by strong alkalis. Ammoniacal environments in particular can produce stress-corrosion cracking in parts that carry residual drawing stresses, so formed components destined for such service should be stress-relief annealed. In seawater, long-term exposure can lead to dezincification, and a more highly alloyed cupro-nickel or aluminium brass grade should be selected for tube and condenser duty.
Typical Applications
Cartridge cases, drawn shells and ammunition components
Clips, fasteners, rivets, springs and hinges
Decorative hardware, architectural trim and name plates
Radiator cores, tanks and heat transfer fins
Electrical connectors, terminals and lamp fittings
General hardware and pressings produced in high volume
FAQ
Q: Is cartridge brass 260 the same as UNS C26000?
Yes. Cartridge brass 260, C260 and UNS C26000 all refer to the same 70/30 copper-zinc alloy, a single-phase alpha brass supplied in many tempers.
Q: How much copper does cartridge brass contain?
The copper content is specified between 68.5 and 71.5 per cent by weight, with zinc making up the remainder. Values quoted as roughly sixty per cent copper refer to other, higher-zinc brasses and do not apply to this grade.
Q: Why is cartridge brass so easy to deep draw?
Because it is a single-phase alpha solid solution with high ductility and a low work-hardening increment per pass, it can accept large reductions between anneals without cracking.
Q: Does cartridge brass need heat treatment to gain strength?
No. Strength comes from cold work. Annealing is used only to restore ductility between forming operations, and the final temper is set by the last cold reduction.
Q: Can cartridge brass be used in seawater?
It resists marine atmospheres and splash exposure, but continuous immersion can cause dezincification. For tube and condenser service in seawater, a cupro-nickel or aluminium brass grade is the better choice.
Q: What machining parameters suit cartridge brass?
Treat it as a moderately machinable brass: use sharp, high-rake tooling, generous feed rates to avoid rubbing, and copious coolant to carry away the stringy chips and control surface finish.
