Leaded Brass is a copper–zinc alloy containing a controlled addition of lead (typically 0.5%–3%) to dramatically improve machinability, surface finish, and pressure tightness.
The lead exists as soft, discrete particles that act as internal lubricants, allowing high cutting speeds, excellent chip breaking, and superior dimensional accuracy. This makes leaded brass one of the most widely used materials for precision-machined components.
Common Grades:
C36000 (Free-Cutting Brass), C38500, C37700, CW614N, CW617N
Typical Chemical Composition
Example: Free-Cutting Brass (UNS C36000)
| Element | Typical % | Function |
|---|---|---|
| Copper (Cu) | 60 – 63 | Base metal, corrosion resistance |
| Zinc (Zn) | 33 – 37 | Strength, hardness, machinability |
| Lead (Pb) | 2.5 – 3.7 | Chip breaking, lubrication |
| Iron / Tin | Trace | Grain control |
Physical Properties
| Property | Typical Value |
|---|---|
| Density | 8.4 – 8.6 g/cm³ |
| Melting Range | 880 – 950 °C |
| Electrical Conductivity | 25 – 30% IACS |
| Thermal Conductivity | 110 – 120 W/m·K |
| Thermal Expansion | ~20 µm/m·°C |
| Magnetic Behavior | Non-magnetic |
| Color | Yellow-gold |
Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 300 – 520 MPa |
| Yield Strength | 120 – 350 MPa |
| Elongation | 10 – 35% |
| Hardness | 80 – 160 HB |
| Modulus of Elasticity | ~100 GPa |
| Machinability Rating | 100% (benchmark alloy) |
Metallurgical Behavior
Leaded brass contains α and β brass phases, with lead present as soft, non-soluble particles. Lead does not increase strength but significantly enhances machinability.
Strengthening occurs mainly through zinc solid-solution strengthening and cold working (drawing, rolling, extrusion). Leaded brass is not heat-treat hardenable.
Role of Lead
Acts as an internal lubricant during cutting
Promotes short, controllable chips
Reduces tool wear
Improves surface finish
Slightly reduces ductility and corrosion resistance
Key Characteristics
✔ Exceptional machinability
✔ High-speed CNC suitability
✔ Excellent dimensional accuracy
✔ Smooth surface finish
✔ Easy soldering and brazing
✔ High productivity at low cost
Limitations:
Not suitable for potable water systems
Lower corrosion resistance than red or naval brass
Poor weldability
Processing Behavior
| Process | Performance |
|---|---|
| Hot extrusion | Excellent |
| Cold drawing | Excellent |
| Machining | Outstanding |
| Forging | Good (C37700) |
| Casting | Limited |
| Welding | Poor |
| Brazing / Soldering | Excellent |
| Plating | Excellent |
Available Forms
Round bars
Hex bars
Flat bars
Rods and wires
Forged blanks
Precision extrusions
Applications
Precision screws, nuts, inserts, and bushings
Plumbing and hydraulic fittings (non-potable)
Electrical terminals and connectors
Automotive fuel and sensor components
Instrumentation and clock parts
Advantages
✔ Best-in-class machinability
✔ Reduced cycle time and tooling cost
✔ Excellent surface quality
✔ Tight dimensional tolerances
✔ Ideal for high-volume production
Why Choose Leaded Brass?
Leaded brass is the optimal choice when machining efficiency, tight tolerances, complex geometries, and superior surface finish are more critical than maximum corrosion resistance.
Comparison with Other Brasses
| Alloy | Machinability | Corrosion Resistance | Typical Use |
|---|---|---|---|
| Cartridge Brass | Good | Good | Formed parts |
| Leaded Brass | Excellent | Moderate | Machined parts |
| Red Brass | Fair | Excellent | Plumbing |
| Naval Brass | Fair | Excellent | Marine |
Compliance & Modern Considerations
Due to environmental and health regulations, leaded brass is restricted in potable water systems, with increasing use of lead-free alternatives.
However, leaded brass remains dominant in industrial machining, automotive, and electrical components due to its unmatched machinability.