C260 Cartridge Brass
Also: C26000, CDA 260, UNS C26000, cartridge brass, 70/30 brass, 70-30 brass, Alloy 260, CuZn30, CW505L, 2.0265, yellow brass (sheet)
C260 is 70/30 cartridge brass, the most ductile common brass: it deep-draws, stamps, spins and takes a bright finish. Sheet and strip for formed parts. Values H02.
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At a glance
| Density | 8.53 g/cm³ (0.308 lb/in³) |
|---|---|
| Tensile strength | 425 MPa (62 ksi) typical H02 strip; annealed about 325-345 MPa (47-50 ksi); spring (H08) about 650 MPa (94 ksi) |
| Yield strength | 360 MPa (52 ksi) typical H02 strip at 0.5% extension; annealed about 105-125 MPa (15-18 ksi) |
| Hardness | 70 HRB typical H02; annealed about 55-65 HRF; hard (H04) about 82 HRB |
| Elongation | 23% typical H02; annealed 55-65%; hard (H04) about 8% |
| Modulus of elasticity | 110 GPa (16 Msi) |
| Thermal | Melts at 915-955 °C (1680-1750 °F); thermal conductivity ~120 W/m·K; electrical conductivity about 28% IACS; expansion ~20 um/m·K |
| Composition | 68.5-71.5% Cu, up to 0.07% Pb, up to 0.05% Fe, balance Zn (about 30%) |
Typical values, H02 (half-hard) strip, 1 mm (0.040") thick; annealed (OS035) and hard figures as noted. Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- About 30% of C360: gummy, with long stringy chips that nest and drag on the finish. Sharp positive-rake tools, high speed, a light lubricant and chip breakers make it workable for secondary operations; do not pick C260 for a turned part.
- WeldabilityFair
- Solders and silver-brazes very well and resistance welds acceptably in thin gauges. Arc welding is troubled by zinc fuming and porosity; TIG with silicon bronze filler works on non-critical joints with good ventilation.
- FormabilityExcellent
- The reference deep-drawing brass: annealed sheet draws cups deeper than one diameter in a single stage, spins, coins and bends flat on itself (0t) in soft temper. Half-hard bends at about 1t. Anneal between severe draws to reset work hardening.
- Corrosion resistanceGood
- Good in atmosphere, fresh water and most dry gases; tarnishes but does not rust. Dezincifies in stagnant, warm, acidic or high-chloride water, and season-cracks in ammonia and amines if residual stress is left in. Stress relieve after forming; plate or lacquer for appearance.
C260 is the 70% copper, 30% zinc alloy that sits at the peak of brass ductility: single-phase alpha, no lead, and the best combination of strength and stretch in the family. It got its name from drawn ammunition cases and still makes them, along with lamp and lighting parts, radiator tanks, plumbing trim, drawn cups and eyelets, spring contacts, musical instruments, nameplates and decorative hardware. It is bought as sheet, strip, coil, wire and tube in tempers from soft annealed to spring.
Annealed it draws deeper than any steel or aluminum sheet; half-hard (H02) it gives about 425 MPa (62 ksi) tensile with 23% elongation, and spring temper reaches about 650 MPa (94 ksi). It work-hardens fast, so multi-stage draws get intermediate anneals. It solders and silver-brazes easily, polishes to a mirror, and takes nickel, chrome, tin and silver plate. Its 28% IACS conductivity is enough for connectors and terminals.
It is a poor machining alloy (about 30% of C360, gummy, long chips), which is why turned brass parts are C360 and formed brass parts are C260. It corrodes by dezincification in aggressive water and by season cracking in ammonia when residual stress is left in: stress relieve drawn parts that will be stored or used near ammonia, amines or moist fertilizer. Fusion welding works poorly because of zinc fuming; solder, braze or resistance weld instead.
Heat treatment
Not hardenable; strength comes from cold rolling at the mill and from cold forming in the shop. Anneal at 425-700 °C (800-1300 °F), with lower temperatures giving finer grain for a smoother drawn surface; specify grain size (ASTM E112) when the drawn finish matters. Stress relieve at 260-300 °C (500-570 °F) for about an hour after drawing or spinning to remove the residual stress that drives season cracking.
Tempers and conditions
- OS015 to OS100 (annealed, by grain size)
- H01 (quarter hard)
- H02 (half hard)
- H04 (hard)
- H06 (extra hard)
- H08 (spring)
Stock forms
- Sheet, strip and coil
- Plate (limited)
- Wire
- Seamless tube
- Rolled bar and flat stock
Relative cost
Tier 3 of 5. About the same as C360 per pound and tracks the copper market; sheet and strip are stocked widely in common gauges. Costs more than 5052 aluminum or 304 stainless sheet for the same part, so it is chosen for formability, conductivity, plating and looks.
Typical applications
- Ammunition cartridge cases and primers
- Lamp bases, lighting trim and reflectors
- Radiator tanks, tubes and heat-exchanger fins
- Plumbing trim, escutcheons and drawn fittings
- Electrical terminals, sockets and spring contacts
- Eyelets, rivets, grommets and fasteners
- Musical instruments, nameplates and decorative hardware
Process compatibility
How C260 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| Deep Drawing | ExcellentExcellent | The reference alloy: cups, shells and cases draw in fewer stages than any steel or aluminum sheet; anneal between severe draws. |
| Metal Stamping | ExcellentExcellent | Blanks, pierces and forms cleanly with fine edges; spring temper for contacts, half-hard for general parts. |
| Progressive Die Stamping | ExcellentExcellent | Terminals, contacts and eyelets run from coil at high rates; call the temper and the grain direction relative to bends. |
| Press Brake Forming | ExcellentExcellent | Soft temper bends flat on itself; half-hard at about 1t, hard at 2-3t. Springback is moderate in the soft tempers. |
| Sheet Metal Fabrication | ExcellentExcellent | Trim, enclosures and decorative panels; keep the protective film on until after forming so the mirror finish survives. |
| Waterjet Cutting | ExcellentExcellent | Clean edges on any gauge with no heat or zinc fume; the usual way to profile plate and thick sheet. |
| Laser Cutting | FairFair | Reflective and zinc-bearing: fiber lasers cut thin gauges with nitrogen up to about 3 mm (1/8"), with some dross and fume; waterjet or punch above that. |
| Plating | ExcellentExcellent | Nickel and chrome for decorative and tarnish protection, tin and silver for contacts; brass plates directly with no strike. |
| Annealing | ExcellentExcellent | Interstage anneals at 425-700 °C reset ductility between draws; specify grain size when the drawn surface must stay smooth. |
| Stress Relieving | GoodGood | An hour at 260-300 °C (500-570 °F) after forming removes the residual stress that causes season cracking near ammonia. |
| CNC Machining | FairFair | Secondary drilling and tapping on formed parts is fine; turned parts should be C360. |
| Welding | FairFair | Solder and silver braze are the joining methods; arc welding fumes zinc and porosities, and is kept to non-critical joints with silicon bronze filler. |
| Screw Machining | PoorPoor | Gummy, long chips and 30% machinability; specify C360 for any turned part. |
| Sand Casting | Not recommendedNot recommended | A wrought-only composition; cast yellow brass parts are C85400 or C85700, which look similar and pour well. |
Design and sourcing tips
- Specify "C26000 per ASTM B36" with the temper (OS035, H02) and thickness; for drawn parts add a grain-size range so the drawn surface stays smooth.
- Design draws for the alloy: draw ratios up to about 2:1 in the first stage, then anneal; tell the shop where intermediate anneals are acceptable.
- Bend soft temper any way you like; bend half-hard at 1t or more and put the bend line across the rolling direction if the part allows.
- Add a stress relief (260-300 °C, 1 h) to the routing on drawn or spun parts, especially anything that will be stored, plated or used near ammonia.
- Use C360 for the turned parts of the same assembly; do not ask a shop to machine C260 bar.
- For potable water, C260 has almost no lead and is usually acceptable, but check dezincification: for aggressive water specify a DZR brass such as C35330 or a silicon brass.
Frequently asked questions
- What is cartridge brass?
- The 70% copper, 30% zinc alloy C26000, named for the drawn ammunition cases it was developed for. It is the most ductile common brass and the standard for deep-drawn, spun and stamped brass parts of every kind, from lamp bases to radiator tanks.
- Can C260 brass be machined?
- It can, at about 30% of the machinability of C360: the chips are long and gummy and the finish suffers. Drilling, tapping and light turning on formed parts are fine with sharp tools and high speed. Any part that is primarily turned should be made from C360 free-cutting brass.
- What is season cracking in brass?
- Stress-corrosion cracking of brass in ammonia, amines or similar environments, driven by residual stress from drawing, spinning or bending. Drawn cartridge cases stored near stables were the first known failures, hence the name. A stress relief at 260-300 °C (500-570 °F) for about an hour after forming, plus keeping ammonia away, prevents it.
- Is C260 brass magnetic?
- No. Copper and zinc are both non-magnetic and C260 contains essentially no iron, so it is fully non-magnetic in every temper. That is one reason it is used in instrument and electrical housings.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B36 and ASTM B19
- Copper Development Association (CDA) alloy data for C26000
- ASM Handbook, Volume 2 and Volume 14B (sheet forming of copper alloys)
- Producer data sheets for brass strip (Olin Brass, Wieland, Aurubis)
