If your part needs higher strength than a standard 360 brass or naval brass but you want to avoid the cost and tooling demands of true aluminum bronze, C67500 manganese bronze — a high-strength, tin-bearing copper-zinc alloy — is frequently the missing middle. It carries enough iron and manganese to form a dispersed hard intermetallic phase that resists abrasion and galling in sliding service, while its zinc-rich brass matrix keeps it far more machinable than C63000 nickel aluminum bronze. The catch is that “manganese bronze” is a misnomer that trips up procurement: despite the name, it is a brass, not a bronze — distinct from the aluminum bronzes such as C63000 nickel aluminum bronze — and its properties depend heavily on the temper you actually receive. This article explains what C67500 is, how it machines, where it beats aluminum bronze and naval brass, and exactly what to put on the drawing before you release it to a machining shop.
Material Identity: A Brass Wearing a Bronze Name
C67500 is classified under the UNS copper alloy system as a high-strength brass, specifically a tin-bearing manganese bronze. The base metal is copper alloyed with roughly 36–41% zinc — squarely a brass by any metallurgical definition. The “bronze” label is historical: early manufacturers added small amounts of tin plus iron and manganese to improve strength and wear resistance, and the trade name “manganese bronze” stuck even though manganese itself is typically only present at a fraction of a percent.
This matters for selection because brass and bronze behave very differently in corrosion service. Unlike the silicone bronzes such as C65500 high-silicon bronze or the aluminum bronzes (C63000, C64200), C67500 is not primarily chosen for seawater corrosion resistance. It is chosen for strength combined with good machinability and moderate corrosion resistance under load — the classic profile for valve stems, worm gears, pump shafts, marine propellers, and heavy-duty bearing retainers.
The wrought grade C67500 is the bar/rod counterpart to the more familiar casting alloy C86500 manganese bronze. If your drawing is for a machined-from-bar component, you want C67500 per the rod-and-bar specification; if the part is cast, the foundry is working from a different (casting) designation and the chemistry tolerances differ.
Designation and Applicable Standards
The primary specification for C67500 in rod, bar, and shape form is ASTM B138/B138M — Standard Specification for Copper-Base Alloy Rod and Bar. This is the document a supplier should cite on the mill certificate when you call out C67500 bar stock. For components that will be hot-forged and then machined, ASTM B124/B124M (copper alloy forging rod and bar) is the relevant sibling document.
On the SAE side, C67500 falls under the UNS copper alloy designation harmonized with SAE J461/J463 (wrought and cast copper alloys). The European nearest-equivalent is a high-strength brass in the CuZnAlMnFe system under EN 12163 (rod for general purposes), but it is a near equivalent — chemistry and mechanical minimums are not identical, so do not treat an EN designation as a drop-in substitute without a documented cross-reference on the drawing.
Chemical Composition per ASTM B138/B138M
The distinguishing chemistry of C67500 is the deliberate combination of iron (for the dispersed hard phase), tin (for corrosion resistance and strength), and a controlled trace of manganese and aluminum. The table below gives the specification ranges; always confirm the exact revision your QA system references.
| Element | C67500 Range (wt%) | Metallurgical Role |
|---|---|---|
| Cu (incl. Ag) | 57.0–60.0 | Base matrix |
| Zn | Remainder (~36–41) | Solid-solution strengthener; defines brass character |
| Fe | 0.35–2.0 | Forms hard iron-rich intermetallic particles for wear resistance |
| Sn | 0.50–1.5 | Improves strength and corrosion resistance |
| Mn | 0.05–0.50 | Deoxidizer; assists in forming the wear-resistant phase |
| Al | ≤ 0.25 | Residual; helps deoxidation and hardens slightly |
| Pb | ≤ 0.20 | Residual impurity, kept low |
The iron content is the key to understanding why C67500 wears well: on cooling, excess iron precipitates as fine, hard, iron-manganese intermetallic particles dispersed through the softer brass matrix. In sliding service these hard particles carry the load while the matrix deforms slightly to embed and trap wear debris, giving a bearing-like combination of strength and conformability that a plain high-brass alloy cannot match.
Delivery Conditions and Typical Mechanical Properties
C67500 is supplied in a range of tempers for rod and bar, and the mechanical properties you actually get depend on the temper, the section size, and whether the product is as-extruded, cold-drawn, or hot-forged. A cold-drawn bar will sit toward the upper end of the ranges below; a large hot-forged blank will sit toward the lower end. Values are typical for wrought rod in the half-hard to hard condition unless otherwise noted, and should be confirmed against the mill certificate for your specific size.
| Property | Typical Value | Notes |
|---|---|---|
| Tensile strength | 450–655 MPa | Higher end for cold-drawn rod |
| Yield strength (0.2% offset) | 205–415 MPa | Temper-dependent |
| Elongation | 15–28% | Lower in hard temper |
| Hardness | 80–95 HRB (soft) to ~90+ HRB | Rockwell B scale |
| Density | ~8.3–8.4 g/cm³ | @ 20 °C |
| Melting range (solidus–liquidus) | ~865–890 °C | Approximate |
For comparison in the same (wrought rod) product form, C67500 offers meaningfully higher tensile strength than free-cutting brass C36000 (CuZn36Pb3, typically ~330–460 MPa) and rather higher strength than naval brass C46400, while remaining much easier to machine than C63000 nickel aluminum bronze. It is not, however, in the same corrosion-resistance class as any of those bronzes in seawater, which is the central selection trade-off.
Corrosion, Wear, and Temperature Behavior
C67500 offers useful resistance to atmospheric corrosion and to many fresh-water and mild industrial environments, and it resists dezincification better than plain high-zinc brasses because of the tin addition. But it is not a seawater-alloy: under sustained exposure to chlorides, the zinc-rich matrix can dezincify and lose strength over time. If the application is submerged marine hardware, the nickel aluminum bronzes (C63000) or silicon bronzes (C65500) are the appropriate choices; C67500 is better suited to shafts, stems, gears, and retainers that are lubricated or intermittently wetted rather than permanently immersed in seawater.
Wear resistance is where C67500 earns its keep. The dispersed iron intermetallic phase gives it measurably better resistance to galling and abrasive wear than a plain brass, which is why it shows up in worm gears, valve stems, and spherical bearing seats. Under boundary lubrication, the hard particles help prevent local welding and seizure. Temperature service is limited by the brass matrix: sustained use is generally confined to roughly the ambient-to-moderate range, and hot-working or soldering requires care because the zinc-rich alloy has a comparatively low solidus.
CNC Machining Difficulty and Chip Control
C67500 machines more like a strong brass than a bronze, which is good news on the shop floor. It is gummier and more ductile than free-cutting brass C36000, so it does not break chips as crisply, but it is far more forgiving than the aluminum bronzes, which are notorious for work-hardening and stringy, abrasive chips. Expect a machinability rating of roughly 55–70% relative to C36000 (the standard 100% reference), depending on the exact heat and section.
The practical challenge is not hardness but chip control and edge build-up. The ductile matrix can smear onto the tool edge (built-up edge) if speeds are too low or the tool is not sharp, producing a poor finish and shortened tool life. A sharp, positive-rake tool with a smooth, low-friction coating is the single most effective countermeasure. Rigid workholding matters because the high strength means heavier cutting forces than a free-cutting brass for the same depth of cut.
Tooling, Parameters, and Coolant: Starting Points, Not Promises
The numbers below are conditional starting references only, not fixed recipes. They assume a rigid CNC lathe or mill, sharp carbide tooling with geometry suited to copper alloys, adequate flood coolant, and sound workpiece fixturing. Machine rigidity, tool brand and geometry, coating, coolant delivery, the specific heat or temper of the bar, and final surface-finish requirements will all shift the optimum — you should always fine-tune from these starting values rather than commit to them on the drawing.
| Operation | Starting Surface Speed | Starting Feed | Notes |
|---|---|---|---|
| Turning | ~120–200 m/min (carbide) | ~0.08–0.25 mm/rev | Sharp positive rake; watch for built-up edge at low speed |
| Milling | ~80–150 m/min (carbide) | ~0.05–0.15 mm/tooth | Climb milling preferred; keep DOC moderate |
| Drilling | ~40–80 m/min (carbide/HSS) | ~0.05–0.20 mm/rev | Peck to clear stringy chips |
Tooling guidance:
- Substrate: Carbide (a general-purpose or non-ferrous-geometry grade) preferred; cobalt HSS is a lower-cost fallback for small runs.
- Coating: An uncoated polished edge or a thin TiN / TiAlN coating; low-friction, smooth surfaces reduce edge build-up on the ductile matrix.
- Coolant: Flood coolant (soluble oil or semi-synthetic) for heat removal and chip evacuation; consistent cooling also helps dimensional stability on long, slender parts.
- Workholding: Rigid clamping and short tool overhangs are more important than raw speed for this alloy’s strength level.
Do not treat surface finish or tolerance as a guaranteed outcome of these parameters. A Ra 0.8–1.6 µm finish is typically achievable with fine feeds and a sharp tool, but the actual result depends on machine condition, tool state, and the specific bar you received. State finish and tolerance requirements explicitly on the drawing and let the shop confirm capability.
Post-Machining and Surface Treatment
C67500 is normally specified and used in the wrought/machined condition and does not rely on heat treatment for its strength, the way a hardenable aluminum bronze might. Common post-processing is limited to cleaning, deburring, light polishing, and — where a specific color or tarnish resistance is needed — a clear lacquer or nickel/chrome plating. If plating is required, specify the plating system and thickness on the drawing, because the zinc-rich brass surface accepts electroplating readily but must be properly cleaned and activated first.
Where C67500 Is Actually Used
Typical applications reflect the strength-plus-machinability profile:
- Valve stems and seats in industrial fluid handling, where sliding wear and galling resistance matter more than seawater immersion.
- Worm gears and worm shafts requiring higher strength than a plain brass gear.
- Pump shafts and impeller hubs in non-corrosive or intermittently wetted service.
- Marine propeller shafting and fasteners in the wrought form, particularly where the component is machined from bar (with seawater exposure assessed case-by-case).
- Bearing retainers and spherical seats where the dispersed iron phase helps resist brass-on-steel galling.
Choosing Between C67500 and Its Neighbors
The decision usually comes down to three candidates, compared at the same product form (wrought rod/bar) and comparable indicators:
| Candidate | Strength | Machinability | Seawater Corrosion | Typical Use |
|---|---|---|---|---|
| C67500 (manganese bronze) | High | Good | Moderate (not marine) | Valve stems, worm gears, shafts |
| C36000 (free-cutting brass) | Moderate | Excellent | Poor–moderate | High-volume turned fittings |
| C63000 (nickel aluminum bronze) | Higher | Difficult | Excellent | Submerged marine, propellers |
Choose C67500 when you need more strength and wear resistance than free-cutting brass but do not need seawater-grade corrosion resistance and cannot justify the higher tooling cost and slower cycle times of nickel aluminum bronze. A “near-equivalent” European brass under EN 12163 may look similar on a datasheet, but chemistry and minimum properties differ — confirm with a documented cross-reference rather than assuming interchangeability, and never substitute without re-validating against the drawing requirements.
Drawing and RFQ Checklist
To get an accurate quote and a part that performs, send these with your inquiry:
- Drawing in a neutral format (PDF or STEP) with all dimensions and critical features called out.
- Material call-out: “C67500 per ASTM B138/B138M” plus the specific temper you require (as-extruded vs. cold-drawn changes the delivered strength).
- Quantity and lot requirements: prototype, small batch, or production volume.
- Tolerances and surface finish: state the tolerance band and any Ra finish target explicitly.
- Plating or coating: if any, specify the system, thickness, and any salt-spray or adhesion requirements.
Specifying the temper and the governing standard up front is the single most common fix for quote delays and wrong-material parts. If you are deciding between C67500 and an aluminum bronze for a shaft, stem, or gear, providing the drawing plus the operating environment (lubricated, intermittently wetted, or submerged) lets an experienced shop recommend the right grade for the function rather than the cheapest one for the drawing.
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