C360 Free-Cutting Brass
Also: C36000, CDA 360, UNS C36000, free-cutting brass, free-machining brass, Alloy 360, SAE CA360, CuZn36Pb3, CW603N, 2.0375, C69300 (lead-free alternative, EcoBrass), C27450 (lead-free alternative)
C360 is the free-cutting brass: 3% lead makes it the 100% machinability benchmark for all metals. Turned fittings, valves and hardware. Not for drinking water. Values H02.
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At a glance
| Density | 8.49 g/cm³ (0.307 lb/in³) |
|---|---|
| Tensile strength | 400 MPa (58 ksi) typical H02 rod; annealed about 340 MPa (49 ksi) |
| Yield strength | 310 MPa (45 ksi) typical H02 rod at 0.5% extension; annealed about 125 MPa (18 ksi) |
| Hardness | 78 HRB typical H02; annealed about 68 HRF |
| Elongation | 25% typical H02; annealed about 50% |
| Modulus of elasticity | 97 GPa (14 Msi) |
| Thermal | Melts at 885-900 °C (1630-1650 °F); thermal conductivity ~115 W/m·K; electrical conductivity about 26% IACS; expansion ~20.5 um/m·K |
| Composition | 60-63% Cu, 2.5-3.7% Pb, up to 0.35% Fe, balance Zn (about 35%) |
Typical values, H02 (half-hard) rod, 25 mm (1") diameter; annealed (O60) figures as noted. Confirm against the mill certificate and the purchase spec.
- MachinabilityExcellent
- The 100% benchmark. Runs at the highest speeds of any common alloy with short, dry chips and mirror finishes; use sharp, uncoated carbide or HSS with zero to slightly positive rake so the tool does not dig in. Chips are worth money, keep them clean and segregated.
- WeldabilityPoor
- Lead makes it hot-short and zinc fumes off in the arc, so fusion welding cracks and porosity are the rule. Solder (excellent) and silver-braze (good, keep it short and cool) instead; resistance welding is not practical.
- FormabilityPoor
- The lead globules open cracks on any real bend; H02 bar tolerates knurling, light staking, crimping and shallow cold heading and nothing more. Formed brass parts use C260 or C272.
- Corrosion resistanceGood
- Good in atmosphere, fresh water, most fuels, oils and mild alkalis; tarnishes but does not rust. Dezincifies in stagnant, warm, acidic or high-chloride water, and stress-corrosion cracks in ammonia and amines when residual stress is left in. Stress relieve or plate for those.
C360 is a 60/40-class brass with about 3% lead. The lead sits as fine, insoluble globules that shear the chip and lubricate the tool, which is why C360 is the reference point for the machinability of every other metal: it is rated 100, with 12L14 steel around 160-170 on the steel scale but well below brass in absolute cutting speed. Screw-machine and Swiss shops turn it at the highest surface speeds of any common alloy, with short chips, mirror finishes and negligible tool wear. Its scrap chips are worth a large share of the bar price, which helps the part price in volume.
It is stocked as round, hex, square and rectangular bar and as extruded shapes, mostly in the half-hard (H02) temper at about 400 MPa (58 ksi) tensile, 78 HRB. Fittings, valve bodies, plumbing and gas hardware, electrical connectors, gears, nozzles, adapters and decorative hardware are turned from it, then often nickel or chrome plated. Corrosion resistance in air and fresh water is good; it dezincifies in stagnant, warm or acidic water and cracks in ammonia (season cracking) when left stressed.
The lead is also its problem. C360 cannot be used for wetted potable-water parts under the U.S. Safe Drinking Water Act (0.25% weighted lead maximum, NSF/ANSI 372); the lead-free substitutes are silicon brasses such as C69300 (EcoBrass) and C87850, and low-lead grades such as C27450, all of which machine at 60-80% of C360. Lead makes it hot-short, so it is not welded, and it is not cold formed beyond knurling and light staking. For bent, drawn or spun parts use C260; for conductivity, C110 or tellurium copper C145.
Heat treatment
Not hardenable; strength comes from cold drawing at the mill. Anneal at 425-600 °C (800-1100 °F) for full softness. Stress relieve at 250-300 °C (480-570 °F) for an hour to prevent season cracking in parts that will see ammonia or that were heavily machined or staked. Do not heat above about 600 °C (1100 °F) in service or the zinc begins to volatilize from the surface.
Tempers and conditions
- H02 (half hard, the standard bar temper)
- H01 (quarter hard)
- O60 (soft annealed)
- M30 (as extruded shapes)
Stock forms
- Round, hex, square and rectangular bar
- Extruded shapes and profiles
- Precision ground rod for Swiss machining
- Tube (limited)
- Forgings are C377 forging brass, not C360
Relative cost
Tier 3 of 5. About 2-3x mild steel bar per pound, tracking the copper market, but the fastest cycle times of any metal and a scrap credit for the chips. A turned brass part usually costs less than the same part in steel or aluminum at volume.
Typical applications
- Screw-machine fittings, adapters and unions
- Valve bodies, stems and seats for gas, fuel and non-potable water
- Electrical connector bodies, terminals and cable glands
- Gears, pinions, worms and clock parts
- Nozzles, orifices and pneumatic components
- Decorative and marine hardware (plated)
- Fasteners, inserts and standoffs
Process compatibility
How C360 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | ExcellentExcellent | The easiest metal to machine; sharp uncoated tooling, high speeds, no coolant needed for most work. |
| Screw Machining | ExcellentExcellent | The classic multi-spindle material: fittings and connector bodies by the million at the highest cycle rates of any alloy. |
| Swiss Machining | ExcellentExcellent | Small precision parts from ground rod; chips stay short in the guide bushing and finishes need no polishing. |
| CNC Turning | ExcellentExcellent | Threads, grooves and bores cut clean; hold size for the alloy's high thermal expansion on long parts. |
| Plating | ExcellentExcellent | The usual finishes: bright nickel and chrome for decorative and wear, tin for solderability, gold over nickel for contacts. The lead needs a clean activation but plating shops do it every day. |
| Nickel Plating | ExcellentExcellent | Bright or satin nickel for hardware and connectors; a copper strike is not needed on brass, a chrome flash goes over it for decorative parts. Can brass be nickel plated? |
| Electroless Nickel Plating | GoodGood | Uniform coverage on threads and bores for wear and corrosion; specify a nickel strike first when the lead content is at the high end. |
| Black Oxide | FairFair | Brass blackens in a copper-alloy bath (a different chemistry from steel black oxide); cosmetic, thin, and it wears off high spots. |
| Vibratory Finishing | GoodGood | Deburrs and brightens turned parts fast; use a mild compound so the lead does not smear into the surface. |
| Bead Blasting | GoodGood | A satin finish for plated or lacquered hardware; light media to keep the edges. |
| Welding | PoorPoor | Hot-short from the lead, with zinc fumes; solder or braze instead, or design a mechanical joint. Can brass be welded? |
| Press Brake Forming | Not recommendedNot recommended | Cracks on the outside of any bend; no sheet is stocked. Form C260 and machine C360. |
| Forging | PoorPoor | Hot-short; the forging brass is C377 (C37700), which machines at about 80% of C360. Specify that for hot-forged valve bodies. |
| Passivation | Not recommendedNot recommended | Nitric and citric passivation are stainless processes and will etch brass. For tarnish protection specify a chromate conversion, a benzotriazole dip or clear lacquer. |
Compare C360
Design and sourcing tips
- Call out "C36000 per ASTM B16, H02" on the drawing; "brass" alone lets a shop substitute a lower-lead or lead-free grade with different machining and plating behaviour, or the reverse.
- If the part touches drinking water, do not specify C360; call C69300 (EcoBrass), C87850 or another NSF/ANSI 372 compliant alloy and expect 20-40% longer cycle times.
- Do not design welds into C360 parts; use threads, press fits, solder or brazing.
- Keep bends and cold forming out of the design; knurls, light staking and roll-formed threads are the limit.
- Add a stress relief (250-300 °C, 1 h) or specify plating for parts that will see ammonia, amines or cleaning chemicals; season cracking shows up months later.
- For long parts, remember brass expands about twice as much as steel with temperature: give clearance in steel housings and inspect at 20 °C.
Frequently asked questions
- Is C360 brass lead-free?
- No. C360 contains 2.5-3.7% lead, which is what makes it free-cutting. It cannot be used for wetted parts in drinking-water systems under the U.S. Safe Drinking Water Act (0.25% lead maximum, NSF/ANSI 372). Lead-free free-machining brasses such as C69300 (EcoBrass) and C87850 replace it there at some cost in machinability.
- Why is C360 brass the machinability standard?
- Because the lead in it gives the ideal chip: short, dry, self-lubricating, with low cutting forces and almost no tool wear, so it runs at the highest cutting speeds of any common alloy. The copper-alloy machinability scale sets C360 at 100 and rates every other copper alloy against it; C260 is 30, C110 is 20, C932 bearing bronze is 70.
- Can C360 brass be welded?
- Not usefully. The lead makes the alloy hot-short so fusion welds crack, and the zinc boils out of the arc and leaves porosity and fumes. Solder it (very well) or silver-braze it (well, if the joint is heated quickly), or design a threaded or pressed joint.
- What is the difference between C360 and C260 brass?
- C360 is 60/40 brass with 3% lead, sold as bar for machining: it cuts beautifully and will not bend. C260 is 70/30 cartridge brass with no lead, sold as sheet and strip for forming: it draws, stamps and spins beautifully and machines poorly. Pick by the process that makes the part.
- Does brass rust or corrode?
- It does not rust, but it tarnishes to brown and can corrode two specific ways: dezincification, where zinc leaches out of the alloy in warm, stagnant or acidic water and leaves a weak copper sponge, and stress-corrosion (season) cracking in ammonia or amine environments when the part carries residual stress. Plating, stress relief and choosing a dezincification-resistant alloy for water handle both.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B16
- Copper Development Association (CDA) alloy data for C36000
- ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials
- Producer data sheets for free-cutting brass rod (Mueller Brass, Wieland Chase)
