Manganese Bronze: Grades, Properties, CNC Machining and Applications

Manganese bronze is a family of high-strength copper alloys widely used for bushings, bearings, gears, lead screw nuts, marine components and other parts exposed to heavy mechanical loads. Despite its name, manganese is not normally the main alloying element. Many commercial manganese bronzes contain a large percentage of zinc and are metallurgically closer to high-strength brass than traditional copper-tin bronze.

This distinction matters when selecting material for a CNC-machined component. Different grades sold under the manganese bronze name can have substantially different compositions, mechanical properties, machinability, corrosion behavior and joining characteristics.

For example, cast C86300 is extremely strong but difficult to machine, while wrought C67500 offers lower strength but substantially better machinability. Similarly, manganese bronze is widely associated with marine service, yet its high zinc content means that dezincification must still be considered in certain seawater environments.

This guide explains how manganese bronze actually behaves in engineering applications and how to select and manufacture it for custom CNC parts.

What Is Manganese Bronze?

Manganese bronze is a trade and engineering name used for several copper-zinc alloys strengthened with elements such as manganese, aluminum and iron. Small quantities of tin, lead or nickel may also be present depending on the specific grade.

Unlike conventional tin bronze, manganese bronze does not necessarily contain tin as a major alloying element. In fact, some common manganese bronzes contain between approximately 22% and 42% zinc.

This is why manganese bronze is also called:

• High-strength yellow brass
• High-tensile brass
• Manganese brass
• High-strength manganese bronze

The terminology can create problems when purchasing raw material. A drawing should therefore specify the actual UNS, EN or equivalent material grade instead of simply stating “manganese bronze.”

What Is Manganese Bronze Made Of?

The composition depends strongly on grade. C86300 is one of the best-known cast manganese bronzes and contains approximately 60–66% copper, 22–28% zinc, 5–7.5% aluminum, 2.5–5% manganese and 2–4% iron.

This composition makes C86300 very different from classic tin bronze such as C90500 or C90700.

Is Manganese Bronze Actually Bronze or Brass?

From a traditional metallurgical definition, alloys containing zinc as the major secondary element would normally be considered brasses.

Commercial naming is less strict. The term manganese bronze became established historically and remains widely used even though alloys such as C86300 and C67500 are fundamentally copper-zinc alloys.

The Copper Development Association classifies cast C86300 with high-strength yellow brasses, while C67500 is listed as Manganese Bronze A among wrought copper alloys.

For CNC procurement, the practical conclusion is simple: do not use color or the word “bronze” to identify the material. Always specify an alloy designation.

What Are the Main Grades of Manganese Bronze?

C86300 Manganese Bronze

C86300 is one of the highest-strength cast copper alloys commonly referred to as manganese bronze.

Depending on casting method, it can provide tensile strength around or above 110 ksi, with sand-cast material commonly showing approximately 225 HB hardness.

Les applications typiques comprennent :

• Heavy-duty bushings
• Rolling-mill screw-down nuts
• Engrenages
• Wear components
• Heavy-load bearings
• Industrial machinery components

Its major disadvantage is machinability. C86300 has a relative machinability rating of only about 8, making it significantly more difficult to machine than common leaded bearing bronze or free-cutting brass.

C86400 Manganese Bronze

C86400 contains substantially more zinc and considerably less aluminum and manganese than C86300. Its strength is therefore lower, but its machinability is much better.

According to comparative Copper Development Association bearing data, C86400 has a machinability index around 65 compared with only 8 for C86300.

This illustrates why the general material name alone cannot predict CNC machining behavior.

C67500 Manganese Bronze A

C67500 is a wrought manganese bronze commonly supplied as rod or similar wrought forms rather than a heavy cast bearing alloy.

Its composition is approximately 57–60% copper with zinc forming most of the balance, along with 0.8–2% iron, 0.5–1.5% tin and a relatively small amount of manganese.

C67500 has a machinability rating of approximately 30. It is therefore much easier to machine than C86300 while still providing useful strength.

C86300 vs C67500: Which Should You Choose?

C86300 should be selected when high compressive strength, wear resistance and load capacity justify the greater machining difficulty.

C67500 may be more economical when the part does not need C86300-level strength and substantial CNC machining is required.

Selecting C86300 simply because it appears to be the “stronger bronze” can unnecessarily increase material, tooling and machining costs.

What Are the Properties of Manganese Bronze?

Haute résistance

High strength is the primary reason engineers choose C86300. It provides much higher strength than many conventional bearing bronzes and can tolerate heavy compressive loading.

High Hardness and Wear Resistance

The aluminum-, iron- and manganese-containing structure produces a hard alloy capable of resisting severe mechanical wear.

This makes C86300 useful for large screw nuts and highly loaded sliding components where softer bronze might deform too quickly.

Good Fatigue Performance

Manganese bronze is suitable for components exposed to repeated loading. However, bearing performance should not be evaluated from fatigue strength alone.

Good Corrosion Resistance With Important Limitations

Manganese bronze can provide good atmospheric and water corrosion resistance, but the high zinc content creates a specific limitation: dezincification.

This issue is especially important in marine applications and is often overlooked in simplified descriptions of manganese bronze.

Is Manganese Bronze Easy to CNC Machine?

The answer depends entirely on the alloy.

C67500 is reasonably machinable. C86400 is considerably easier. C86300 is difficult.

C86300’s machinability rating of approximately 8 is extremely low compared with C93200 bearing bronze, which is commonly assigned a rating near 100 on the same relative system.

The combination of high hardness, strength and wear-resistant intermetallic phases increases cutting forces and accelerates cutting-edge wear.

CNC Turning C86300

Many C86300 components are cylindrical bushings, large nuts, sleeves or bearing components, so CNC turning is frequently required.

Rigid machine setup is important. Tool overhang should be minimized because high cutting forces can promote vibration and unstable surface finish.

Carbide tooling is normally more suitable than HSS for production machining. Sharp, stable cutting edges help reduce rubbing and excessive heat.

Manufacturers should also avoid selecting cutting parameters from generic “bronze” charts. A feed and speed suitable for C93200 can be completely inappropriate for C86300.

CNC Milling C86300

Milling creates similar challenges. High tool engagement combined with insufficient rigidity may cause cutter chipping or accelerated flank wear.

Large pockets can also require substantial machining time because aggressive material-removal parameters may shorten tool life.

During DFM review, unnecessary deep pockets and extremely small internal corner radii should therefore be reconsidered when function allows.

Perçage et filetage

Drilling should emphasize tool rigidity and chip evacuation, especially for deep holes.

Threading high-strength manganese bronze also requires attention because large cutting forces can damage the tool or produce poor thread quality.

For large lead screw nuts, thread geometry, surface finish and mating screw condition can be more important to service life than simply meeting the nominal thread dimensions.

Why Is C86300 Used for Heavy-Duty Bearings?

The Copper Development Association identifies C86300 and C86400 as manganese bronze bearing alloys capable of operating at relatively high speeds under heavy loads.

The reason is their combination of high compressive strength and wear resistance.

However, there is a major design trade-off.

High-strength bronze does not conform easily to shaft misalignment and does not embed abrasive contamination as effectively as soft leaded bearing bronze.

This means C86300 generally requires:

• A hard mating shaft
• Good shaft surface finish
• Reliable lubrication
• Good alignment
• Clean lubricant
• Protection from abrasive contamination

A designer should therefore not replace C93200 with C86300 solely to increase bearing strength without reviewing the complete bearing system.

Is Manganese Bronze Self-Lubricating?

This phrase needs qualification.

Some descriptions characterize manganese bronze as self-lubricating because certain grades contain lead and copper alloys can offer favorable anti-seizing characteristics.

That does not mean every solid manganese bronze bushing should operate without external lubrication.

C86300 permits only a very small lead content, while grades such as C86400 may contain considerably more lead. Their tribological behavior is therefore not identical.

For a heavily loaded C86300 bearing, lubrication should normally be treated as part of the bearing design unless the system has specifically been validated for dry operation.

Why Is Shaft Hardness Important?

Hard manganese bronze bearings require a correspondingly suitable shaft.

If a soft shaft is paired with a hard, heavily loaded bronze bushing, the shaft itself can become the sacrificial wear surface.

This defeats one of the main reasons for using a replaceable bronze bearing.

The correct shaft hardness depends on alloy, pressure, velocity, lubricant and surface condition. Engineers should review these variables together instead of specifying only a bronze grade.

What Is PV and Why Does It Matter?

Bearing selection is not based on load alone.

PV combines bearing pressure (P) and sliding velocity (V). A bushing operating under a very high static load at low speed does not experience the same thermal and lubrication conditions as the same bushing under moderate load at much higher speed.

As PV increases, frictional heat becomes more important.

Consequently, statements such as “C86300 is suitable for high loads” should never be interpreted as unlimited bearing capacity.

Engineers should also consider:

• Lubrication method
• Cycle de service
• Température de fonctionnement
• Oscillating versus continuous rotation
• Shaft hardness
• Misalignment
• Contamination

Can Manganese Bronze Be Used in Seawater?

Yes, but this question requires more care than many general material guides suggest.

Manganese bronze has historically been used for:

• Marine propellers
• Shafts
• Deck fittings
• Winches
• Marine hardware

However, many manganese bronze grades contain more than 15% zinc. High-zinc copper alloys can suffer selective zinc removal in seawater, known as dezincification.

What Is Dezincification of Manganese Bronze?

Dezincification is a corrosion mechanism in which zinc is selectively removed from a copper-zinc alloy.

The remaining region can become porous and copper-rich. A component may retain its external shape while losing substantial mechanical integrity.

This explains a failure mode sometimes seen in old marine propellers: the outside may appear reddish or copper-colored while the underlying structure has become weakened.

Copper Development Association marine guidance specifically identifies manganese bronze among high-zinc alloys that can be susceptible to this mechanism.

Tin additions can reduce the tendency, and cathodic protection can provide additional protection in appropriately designed marine systems.

Therefore, manganese bronze should not simply be described as “corrosion-resistant in seawater” without considering:

• Exact alloy
• Water chemistry
• Flow velocity
• Stagnant conditions
• Cathodic protection
• Galvanic coupling
• Service life requirement

Manganese Bronze vs Aluminum Bronze

These alloys are frequently compared because both offer considerably higher strength than conventional bearing bronzes.

Nickel aluminum bronze is often preferred for demanding modern marine propellers because of its strength and corrosion performance.

Manganese bronze can remain appropriate for medium-duty marine applications, but material selection should consider dezincification and galvanic conditions.

Manganese Bronze vs Tin Bronze

Tin bronze such as C90500 and C90700 has a copper-tin-based composition and is widely used for bearings, gears and corrosion-resistant mechanical components.

Manganese bronze such as C86300 obtains substantially greater strength through its zinc-, aluminum-, iron- and manganese-containing structure.

Select C86300 when high load capacity and mechanical strength are dominant requirements.

Select a conventional tin bronze when the application requires a different balance of conformability, corrosion resistance, machinability and wear behavior.

Manganese Bronze vs C93200 Bearing Bronze

C93200 and C86300 illustrate two very different bearing strategies.

C93200 is softer, contains significant lead and is extremely easy to machine. It provides good embeddability, anti-seizing behavior and tolerance of less-than-perfect operating conditions.

C86300 is much stronger and harder but requires cleaner lubrication, better alignment and a harder shaft.

In practical terms:

• Use C93200 for many general-purpose bushings.
• Consider C86300 when loads become too high for softer bearing bronze.
• Do not assume C86300 is an automatic upgrade in every bearing system.

Does Casting Method Affect C86300 Parts?

Yes. C86300 can be produced by sand casting, centrifugal casting and continuous casting.

Casting method influences stock geometry, mechanical properties, machining allowance and the distribution of casting defects.

For cylindrical bushings and rings, centrifugal casting can be attractive because the raw shape is closer to the final component than a solid rectangular billet.

For long production runs, continuous-cast material may also offer useful consistency.

Regardless of casting process, designers should recognize that porosity, inclusions and shrinkage can originate in the casting and may only become visible after CNC machining removes the external skin.

A machinist cannot repair internal casting porosity simply by changing feeds and speeds.

Can Manganese Bronze Be Welded?

Weldability varies dramatically by alloy.

C86300 is particularly difficult for several conventional joining methods. Copper Development Association data rates soldering, brazing, oxyacetylene welding and gas-shielded arc welding as poor, while coated metal arc welding is rated good.

The high zinc content is one reason joining can be troublesome. Excessive heat can cause zinc evaporation and unstable weld behavior.

A recent welding forum discussion described exactly this problem: a user attempting TIG repair on a manganese bronze casting found that zinc volatilization repeatedly disrupted the molten region.

C67500 behaves very differently. It is rated excellent for soldering and brazing and good for several other joining processes.

Again, “manganese bronze” is not specific enough to determine the manufacturing process.

What Surface Finishes Are Used on Manganese Bronze?

Machined Finish

Most functional bushings, nuts and wear components use the machined surface directly.

Bearing surfaces should be specified based on the required shaft interaction rather than cosmetic appearance.

Polissage

Manganese bronze can be polished for architectural or decorative components. Its yellow-brown color can produce an attractive metallic finish.

Protective Clear Coating

Clear coatings may be used where preserving a polished decorative appearance is more important than allowing natural patina formation.

Plaquage

Plating may be specified for specialized engineering purposes, but coating thickness must be considered on precision bearing and mating surfaces.

What CNC Parts Are Made From Manganese Bronze?

Common CNC-machined manganese bronze parts include:

• Heavy-duty bushings: Support shafts under high mechanical loads.
• Large lead screw nuts: Used in presses, rolling mills and heavy positioning systems.
• Wear plates: Provide replaceable high-strength sliding surfaces.
• Engrenages : Used where strength and wear resistance are required.
• Valve components: Combine mechanical strength with useful corrosion resistance.
• Marine hardware: Includes fittings, shafts and selected propeller applications.
• Thrust components: Resist heavy axial loads.
• Industrial bearing components: Used where softer bearing bronze lacks sufficient strength.

What Factors Affect the Cost of CNC Machining Manganese Bronze?

Exact Alloy Grade

C86300 requires much more machining effort than C67500 or C86400. Alloy selection therefore directly affects cycle time and tool consumption.

Raw Material Form

Using a hollow cast tube for a large bushing can reduce both copper-alloy material waste and machining time.

Deep Material Removal

Large pockets and thick stock create high tooling cost when machining a hard grade such as C86300.

Internal Threads

Large precision lead screw nuts can require significant machining and inspection time, especially when thread surface finish is important.

Tight Bearing Tolerances

Close bore tolerance, cylindricity, concentricity and surface-finish requirements increase final machining and inspection time.

Casting Quality

Internal casting defects can cause scrap after substantial machining has already been completed. Raw-material quality therefore influences total project cost.

How Should Manganese Bronze Be Specified on a Drawing?

A drawing should not state only “manganese bronze.” It should include the exact alloy whenever possible.

Useful requirements include:

• UNS or EN material designation
• Applicable ASTM or other material standard
• Cast or wrought form
• Critical dimensions
• Rugosité de surface
• Geometric tolerances
• Bearing clearance
• Spécification du filetage
• Material certification
• Acceptable casting-defect criteria
• Exigences d’inspection
• Surface treatment requirements

For marine components, corrosion environment and cathodic-protection conditions should also be considered during material selection.

Common Questions About Manganese Bronze

Does Manganese Bronze Rust?

It does not rust in the same way as carbon steel because iron is not its base metal. It can still corrode through other mechanisms, including dezincification.

Is Manganese Bronze Stronger Than Regular Bronze?

C86300 is considerably stronger than many traditional bearing and tin bronzes. However, “bronze” covers many alloy families, so exact grades should be compared.

Why Is C86300 So Difficult to Machine?

Its high hardness, strength and wear-resistant microstructure produce high cutting forces and rapid tool wear. Its published relative machinability rating is only about 8.

Can Manganese Bronze Be Used for Bushings?

Yes, particularly for high-load applications. It requires proper shaft hardness, alignment, surface finish and lubrication.

Does Manganese Bronze Need Lubrication?

Do not assume a solid C86300 bushing can operate dry. Most heavy-load bearing applications require an appropriate lubrication strategy.

Can Manganese Bronze Be TIG Welded?

Some manganese bronze grades are difficult to TIG weld because of their high zinc content. C86300 is rated poorly for gas-shielded arc welding, so the exact grade and approved repair procedure should be confirmed first.

Why Did an Old Manganese Bronze Propeller Turn Red?

A reddish copper-rich region can be a sign of dezincification, where zinc has selectively leached from the alloy. The remaining material can be porous and mechanically weakened.

CNC Machining Manganese Bronze at Tuofa CNC Germany

Manganese bronze is a good example of why selecting a material by family name alone can create unnecessary manufacturing problems.

A heavy-load component may genuinely require C86300, while another part can achieve its functional requirements with the more machinable C67500 or another bearing bronze. The difference can significantly affect tool life, machining time and final cost.

Tuofa CNC Germany provides CNC turning, CNC milling, drilling, boring and threading for custom copper-alloy components. During DFM review, material grade can be evaluated together with wall thickness, bearing geometry, thread design, tolerances, surface roughness and mating components.

For cast manganese bronze parts, machining allowance and the possibility of casting defects should also be considered before critical dimensions are finalized.

Customers can provide a 3D CAD file and 2D engineering drawing together with the required manganese bronze grade, quantity and operating conditions. For bearings, bushings and lead screw nuts, information about load, shaft material, lubrication and assembly conditions can help determine whether the requested material is appropriate.

Conclusion

Manganese bronze is not simply a conventional bronze with extra manganese. Most important engineering grades are high-strength copper-zinc alloys containing additional aluminum, iron and manganese.

C86300 provides exceptional strength, hardness and load capacity but is difficult to CNC machine, with a machinability rating of approximately 8. C67500 provides a different balance, sacrificing some strength while offering substantially better machinability and joining characteristics.

For bearing applications, high strength must also be balanced against shaft hardness, alignment, lubrication and contamination. For marine applications, engineers must consider dezincification rather than assuming that every manganese bronze grade is immune to seawater corrosion.

Choosing the correct alloy therefore requires more than comparing tensile strength. Composition, product form, machining cost, bearing conditions, corrosion environment and joining requirements should all be evaluated together before production.