Leaded bronze is a copper-based bearing alloy containing intentionally added lead, usually together with tin and sometimes zinc or nickel. The soft lead phase improves machinability, conformability and resistance to seizure, which is why leaded bronze is widely used for bushings, plain bearings, thrust washers and other sliding components.
However, “leaded bronze” covers several alloy families rather than one fixed composition. The lead content, tin content and casting condition must all be considered before a grade is selected.
What Is Leaded Bronze Made Of?
Most cast leaded bearing bronzes contain copper, tin and lead. Tin strengthens the copper-rich matrix, while lead remains largely insoluble and forms soft, dispersed particles throughout the alloy. Zinc, nickel, iron and other elements may also be present in controlled amounts.
This explains why some materials are described as both leaded bronze and high-leaded tin bronze. C93200, for example, belongs to the copper-tin-lead family and is commonly called SAE 660 bearing bronze.
The terminology should still be used carefully:
- Tin bronze emphasizes tin as the principal alloying element.
- Leaded tin bronze identifies a copper-tin alloy containing intentional lead.
- Leaded bronze is a broader commercial term for bronze bearing alloys containing lead.
- Leaded brass normally contains considerably more zinc and should not automatically be treated as an equivalent material.
See What Is Tin Bronze? for a closer explanation of the tin-bronze family, or What Is a Copper Alloy? for the wider material classification.
How Does Lead Change Bronze Properties?
Lead changes both the manufacturing characteristics and bearing behavior of bronze.
The dispersed lead phase makes the alloy easier to cut, reducing cutting forces and helping manufacturers produce precise bores, grooves and other machined features. This is particularly useful for large bushings and parts with tight dimensional tolerances.
Lead also improves conformability. A leaded bronze bearing can accommodate small alignment errors and slight shaft deflection more readily than a harder, less conformable material. Its embeddability allows small contaminant particles to become trapped below the working surface instead of continuously scoring the mating shaft.
Under boundary-lubrication conditions, the soft lead phase can reduce friction and improve resistance to galling or seizure. This does not mean that every leaded bronze bearing is self-lubricating. Most applications still require properly selected oil, grease or another lubrication system.
These benefits involve trade-offs. Increasing the lead content generally reduces tensile strength, hardness and load capacity. High-lead grades may therefore provide excellent machinability and anti-seizure behavior but may not be suitable for the highest structural loads. Corrosion resistance also depends on the complete alloy and operating medium, not simply on whether lead is present.
Common Leaded Bronze Grades and Typical Data
The following table compares four cast copper-tin-lead alloys. Composition ranges and minimum tensile values are based on Copper Development Association data. The tensile values shown apply to the as-continuous-cast M07 condition at room temperature.
| UNS grade | Copper | Lead | Tin | Minimum tensile strength |
|---|---|---|---|---|
| C93200 / SAE 660 | 81–85% | 6–8% | 6.3–7.5% | 35 ksi / 241 MPa |
| C93400 | 82–85% | 7–9% | 7–9% | 34 ksi / 234 MPa |
| C93700 / SAE 64 | 78–82% | 8–11% | 9–11% | 35 ksi / 241 MPa |
| C93800 / SAE 67 | 75–79% | 13–16% | 6.3–7.5% | 25 ksi / 172 MPa |
C93200 is a general-purpose bearing bronze offering a practical balance of machinability, strength and frictional performance. C93400 contains similar amounts of tin and lead and is used for bearings, bushings, washers and pump components.
C93700 contains more tin and lead and is commonly associated with bearing and corrosion-resistant applications. C93800 has a higher lead content, providing excellent machinability and conformability but lower tensile strength.
These values are material references, not a complete list of grades supplied by JEDBUSHING. Mechanical properties change with casting method, section size and test condition. Purchase specifications should therefore identify the required standard, grade, casting process and acceptance criteria.
Where Is Leaded Bronze Used?
Leaded bronze is primarily used where a component slides or rotates against a shaft, pin or guide surface. Common applications include:
- Plain and sleeve bearings
- Flanged bushings
- Thrust washers and thrust bearings
- Bearing plates and slide plates
- Pump and valve bushings
- Hydraulic equipment components
- Rolling-mill and machine-tool bearings
- Mining and earthmoving machinery
- Crane, press and gearbox components
Some leaded bronze alloys are also used as the bearing layer in bimetal bearings, where the bronze provides the working surface and a steel backing supplies structural support.
The exact alloy cannot be selected from the application name alone. A pump bushing, for example, may require different material properties depending on the fluid, shaft material, load, speed, lubrication and operating temperature.
How Should Engineers Choose a Leaded Bronze Grade?
Material selection should begin with operating conditions rather than a familiar alloy designation.
The main factors include:
- Load and speed: Confirm the actual bearing pressure, sliding speed and resulting PV value.
- Lubrication: Identify the lubricant, supply method, expected film condition and possibility of interrupted lubrication.
- Shaft condition: Shaft hardness, surface finish, alignment and runout influence wear and seizure risk.
- Contamination: Dirt or embedded particles may make conformability and embeddability especially important.
- Operating environment: Temperature, chemicals, seawater and process fluids must be evaluated separately.
- Required strength: A higher-lead alloy is not automatically better when the part must carry heavy structural loads.
- Regulatory requirements: Drinking-water, food-contact and other lead-restricted applications may require a verified lead-free alternative.
- Manufacturing route: Centrifugal, continuous and permanent-mold castings can have different structures and specified properties.
Where operating data are incomplete, the manufacturer should review the drawing together with the shaft, lubrication and service conditions before confirming the grade.
Custom Leaded Bronze Castings from JEDBUSHING
JEDBUSHING manufactures custom leaded bronze bushings and other copper-alloy components according to customer drawings or samples. Available product forms include sleeve and flanged bushings, thrust washers, rings, bronze wear plates and custom bronze parts.
Depending on the part geometry, quantity and material requirements, production may use centrifugal casting, horizontal continuous casting or vertical permanent-mold casting. Castings can then be CNC machined and inspected for chemical composition, dimensions and drawing-specific requirements. More information about our manufacturing and inspection capabilities is available on the About JEDBUSHING page.
To request a technical review, send the drawing, alloy specification, quantity and operating conditions through our contact page. If the application restricts lead, state that requirement before material selection so that an appropriate lead-free alternative can be considered.
FAQs About Leaded Bronze
Is leaded bronze magnetic?
Leaded bronze is generally considered non-magnetic because copper, tin and lead are non-ferromagnetic. Small amounts of other elements or nearby steel components may affect an instrument reading, but the bronze itself should not behave like carbon steel.
Can leaded bronze be welded?
Welding is generally not recommended for many high-leaded cast bronze grades. Lead can cause porosity, cracking and fume hazards during welding. Suitability depends on the exact alloy and repair procedure, while soldering or brazing may be possible for certain grades.
Is leaded bronze the same as leaded brass?
No. Most leaded bearing bronzes use copper and tin as the primary metallic system, while leaded brass contains a significant amount of zinc. Commercial names sometimes overlap, so material should be identified by a recognized UNS, ASTM, EN or other applicable grade.
How can the lead content in bronze be verified?
X-ray fluorescence can provide rapid alloy screening, while optical emission spectroscopy or another validated laboratory method can confirm composition. Because lead segregation may occur in cast material, critical components may require samples or measurements from more than one location.
Can leaded bronze scrap be recycled?
Yes. Leaded bronze can be recycled through a controlled copper-alloy scrap stream. It should be separated from lead-free copper alloys, identified by grade where possible and handled by a recycler equipped to manage lead-containing material safely.