Brass is copper alloyed with zinc, and the zinc content decides everything. Below about 35% zinc the alloy is single-phase alpha — superbly ductile, deep drawable, relatively dezincification-resistant; above about 37% a second beta phase appears and the alloy becomes stronger, far more hot workable and far more machinable, at the cost of cold formability and corrosion resistance. Add lead and machinability climbs from 20 to 100: C36000 free-cutting brass is the 100 on the CDA machinability scale, the benchmark against which every other metal is measured. Add tin and you get the naval brasses; add an arsenic or antimony inhibitor and you get the condenser-tube grades C44400 and C68700. The 30 grades below run from 95% copper gilding metal to a 758 MPa cast manganese bronze. Four are covered by ASTM F468 and F467 as certified fastener alloys.
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Zinc sets the structure, and the structure sets the behaviour. Below roughly 35% zinc brass is single-phase alpha: face-centred cubic, outstandingly ductile, cold formable to severe reductions and relatively resistant to dezincification. Above roughly 37% zinc a second beta phase appears and the alloy becomes alpha-beta — stronger, dramatically more hot workable, markedly more machinable, and considerably more vulnerable to selective zinc attack. Cold formability runs the other way: C26000 cartridge brass will take deep drawing that would crack a Muntz metal. If the part is deep drawn, specify an alpha brass. If it is hot forged or heavily machined, specify an alpha-beta one.
Dezincification is brass's characteristic failure mode. In stagnant, warm, slightly acidic or high-chloride water the zinc is selectively leached out, leaving a porous copper residue that keeps the original shape and dimensions of the part. A dezincified fitting can look perfectly sound and crumble under hand pressure, and plug-type attack can perforate a wall while the surrounding metal appears untouched. Alpha brasses below about 15% zinc are essentially immune; alpha brasses to 35% zinc are moderately resistant; alpha-beta brasses above 37% zinc are the vulnerable ones. The answer is inhibition — C44400 carries 0.02–0.10% antimony and C68700 carries 0.02–0.06% arsenic, and both are condenser-tube alloys for exactly that reason. Where a brass will see potable water, seawater or stagnant warm aqueous service, specify an inhibited or DZR grade and expect to prove it by ISO 6509 testing.
Season cracking is the other classic failure, and it is named after the monsoon. Cold-worked brass cartridge cases stored in Indian arsenals cracked spontaneously during the humid season; the cause was traced to traces of ammonia acting on metal carrying high residual tensile stress. The mechanism is unchanged. Moist ammonia, ammonium compounds, amines, nitrites and mercury compounds will crack a stressed brass component, and the higher the zinc and the higher the residual stress, the faster it happens. The control is a low-temperature stress-relief anneal after cold forming, and on brass it is not optional — specify it as standard on deep-drawn, heavily formed, swaged or tightly threaded parts going into service.
Lead makes brass the most machinable engineering metal there is — and it is the element under the most regulatory pressure. Lead is essentially insoluble in the copper-zinc matrix, so it sits as discrete soft globules that break the chip and lubricate the cut. The grades here run the full scale as lead rises from nil to 3.5%: 20 for gilding metal, 30 for the unleaded alpha brasses, 40 for Muntz metal, then 60, 70, 90 and 100 for C36000. The regulatory position has changed and continues to change. Lead in drinking-water-contact components is restricted under the US Safe Drinking Water Act, which cut the wetted-surface limit to a weighted average of 0.25%, and under the European Drinking Water Directive and national acceptance schemes; lead in electrical and electronic equipment is restricted under RoHS, where the copper-alloy exemption has been progressively narrowed. A leaded brass specified without question twenty years ago may now be unusable in the same application. Confirm the position for your market before committing a design to a leaded brass.
Four brasses here are certified fastener alloys. ASTM F468 and F467 list C26000 as Cu 260, C27000 as Cu 270, C46200 as Cu 462 and C46400 as Cu 464 — the two cartridge and yellow brasses and the two naval brasses. Those are the grades to specify where a certified brass bolt, stud or nut is required, and the naval brasses are the sensible default for marine bolting. The other twenty-six are supplied to their mill product standards — ASTM B36, B111, B124, B134, B135, B171, B21, B283, B371, B455, B584 and others as applicable. Brass fasteners are chosen for machinability, corrosion resistance in mild environments, appearance, non-sparking behaviour and conductivity rather than load: a naval brass bolt develops around 400 MPa against 830 MPa for an ASTM A325 steel one. Where higher strength is needed in a copper alloy, see beryllium copper.
Brass spans the entire machinability scale, and grade choice dominates every other variable. The unleaded alpha brasses rate 20 to 30 — gummy, prone to built-up edge, producing long stringy swarf that needs chip breakers and generous coolant. Adding beta phase lifts that to around 40; adding lead takes it to 60, 70, 90 and 100 for C36000, where the chip breaks mechanically into short crumbs, tool life is outstanding and cutting speeds are the highest of any engineering metal. On the forming side the ranking inverts: the alpha grades deep draw, spin and cold head, while the alpha-beta grades hot forge — and C37700 is the 100 on the CDA forgeability scale, the reference alloy for hot forging in the same way C36000 is for machining. Use positive rake, sharp tooling and free-flowing coolant on the unleaded grades, and stress relieve every cold-formed part before it goes into service.
All composition and machinability data from the Copper Development Association alloy records. Copper and lead figures are read directly from the individual grade pages. Machinability is on the CDA scale where C36000 = 100.
| Grade | Common Name | Family | Copper % | Lead % | Structure | Machinability | Chosen For |
|---|---|---|---|---|---|---|---|
| C21000 | Gilding Metal 95% | Plain alpha | 94.0–96.0 | 0.05 max | Single-phase alpha | 20 | Colour and deep forming; 56% IACS — highest here |
| C22000 | Commercial Bronze 90% | Plain alpha | 89.0–91.0 | 0.05 max | Single-phase alpha | 20 | Decorative hardware, grillwork, screens |
| C22600 | Jewelry Bronze 87.5% | Plain alpha | 86.0–89.0 | 0.05 max | Single-phase alpha | 30 | Jewellery, badges, fine formed work |
| C23000 | Red Brass 85% | Plain alpha | 84.0–86.0 | 0.05 max | Single-phase alpha | 30 | Plumbing pipe, condenser and heat exchanger tube |
| C24000 | Low Brass 80% | Plain alpha | 78.5–81.5 | 0.05 max | Single-phase alpha | 30 | Deep drawing, flexible hose, spinning |
| C26000 | Cartridge Brass 70% | Plain alpha | 68.5–71.5 | 0.07 max | Single-phase alpha | 30 | The deep-drawing brass; ASTM F468 Cu 260 |
| C26800 | Yellow Brass 66% | Plain alpha | 64.0–68.5 | 0.09 max | Single-phase alpha | 30 | General forming and stamping |
| C27000 | Yellow Brass 65% | Plain alpha | 63.0–68.5 | 0.09 max | Single-phase alpha | 30 | General forming; ASTM F468 Cu 270 |
| C27200 | Yellow Brass 63% | Plain alpha | 62.0–65.0 | 0.07 max | On the alpha/alpha-beta boundary | — | The alpha / alpha-beta boundary composition |
| C28000 | Muntz Metal 60% | Plain alpha-beta | 59.0–63.0 | 0.09 max | Alpha-beta | 40 | Hot rolling, condenser plate, architectural sheet |
| C33000 | Low Leaded Brass Tube | Leaded | 65.0–68.0 | 0.25–0.7 | Single-phase alpha | 60 | Machined tubular components |
| C33500 | Low Leaded Brass | Leaded | 62.0–65.0 | 0.25–0.7 | Single-phase alpha | 60 | Stamped flat parts needing secondary machining |
| C34000 | Medium Leaded Brass | Leaded | 62.0–65.0 | 0.8–1.5 | Single-phase alpha | 70 | Forming plus machining — the middle ground |
| C34200 | High Leaded Brass 64.5% | Leaded | 62.0–65.0 | 1.5–2.5 | Single-phase alpha | 90 | High-volume machined parts, some forming |
| C35300 | High Leaded Brass 62% | Leaded | 60.0–63.0 | 1.5–2.5 | Alpha-beta | 90 | Hot formed then heavily machined |
| C35600 | Extra-High-Leaded Brass | Leaded | 60.0–63.0 | 2.0–3.0 | Alpha-beta | 100 | Blanked and machined flat parts at mach 100 |
| C36000 | Free-Cutting Brass | Leaded | 60.0–63.0 | 2.5–3.0 | Alpha-beta | 100 | The 100 on the machinability scale |
| C37000 | Free-Cutting Muntz Metal | Leaded | 59.0–62.0 | 0.8–1.5 | Alpha-beta | 70 | Machined tube and hot-formed parts |
| C37700 | Forging Brass | Leaded | 58.0–61.0 | 1.5–2.5 | Alpha-beta | 80 | The 100 on the forgeability scale |
| C37710 | Leaded Forging Brass | Leaded | 56.5–60.0 | 1.0–3.0 | Alpha-beta | — | Wide-tolerance forging stock — composition only |
| C38500 | Architectural Bronze | Leaded | 55.0–59.0 | 2.5–3.5 | Alpha-beta | 90 | Extruded architectural shapes and sections |
| C44400 | Admiralty, Antimonial | Tin, inhibited | 70.0–73.0 | 0.07 max | Single-phase alpha | 30 | Condenser tube — Sb inhibited |
| C46200 | Naval Brass 63½% | Naval | 62.0–65.0 | 0.20 max | Alpha-beta | — | Marine bolting; ASTM F468 Cu 462 |
| C46400 | Naval Brass, Uninhibited | Naval | 59.0–62.0 | 0.20 max | Alpha-beta | 30 | The standard naval brass; F468 Cu 464 |
| C47940 | Leaded Tin Brass | Naval | 63.0–66.0 | 1.0–2.0 | Alpha-beta | — | ASTM B21 bar — composition only |
| C48200 | Naval Brass, Medium Leaded | Naval | 59.0–62.0 | 0.40–1.0 | Alpha-beta | 50 | Machined marine components |
| C48500 | Naval Brass, High Leaded | Naval | 59.0–62.0 | 1.3–2.2 | Alpha-beta | 70 | Screw-machine work for marine service |
| C68700 | Aluminum Brass, Arsenical | Tin / Al, inhibited | 76.0–79.0 | 0.07 max | Single-phase alpha | 30 | High-velocity seawater; As inhibited |
| C69400 | Silicon Red Brass | Silicon | 80.0–83.0 | 0.30 max | Silicon-strengthened | 30 | Strongest wrought grade — 690 MPa |
| C86300 | Manganese Bronze, Cast | Cast | 60.0–66.0 | 0.20 max | Cast alpha-beta | 8 | Strongest here — 758 MPa min, CAST |
Read the table left to right and the logic falls out. Copper content sets the structure: the alpha grades at the top deep draw and resist dezincification, the alpha-beta grades below hot forge and machine. Lead sets machinability, from 20 at the top to 100 at C36000 and C35600, the two highlighted free-machining grades, alongside C37700, which is the 100 for forgeability rather than machinability. The two inhibited grades, C44400 and C68700, are the ones to specify for condenser and seawater tube. The four marked grades are the ASTM F468 and F467 certified fastener alloys. Two grades are registered on composition alone — CDA publish no mechanical or physical data for C37710 or C47940, and we have not substituted figures from their nearest relatives. Three entries are not, strictly, wrought brasses: CDA class C68700 and C69400 as wrought bronzes, and C86300 is a cast manganese bronze, available only as castings and cast bar. All three are listed here because they are copper-zinc alloys bought alongside the brasses, but the designation should be used correctly on drawings.
We are committed to delivering zero-defect brass fasteners and components. All products undergo rigorous testing including PMI (Positive Material Identification), chemical analysis with copper, zinc, lead and tin contents certified explicitly — lead content determines drinking-water and RoHS acceptability and must be stated on the certificate — mechanical and hardness verification against the specified temper and section, ISO 6509 dezincification testing where required, stress-relief confirmation on cold-formed parts, dimensional inspection and full traceability with EN 10204 3.1 certification.
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