Free Machining Brass, commonly designated as C36000 (C360), is a copper–zinc alloy engineered specifically for superior machinability. Its high lead content enables excellent cutting performance, low tool wear, and high production efficiency.
Recognized as the easiest metal to machine, free machining brass is the preferred choice for high-speed automatic lathes and precision components requiring tight tolerances and smooth surface finishes.
Chemical Composition (C36000)
| Element | Content (wt%) |
|---|---|
| Copper (Cu) | 60 – 63 |
| Zinc (Zn) | 35 – 38 |
| Lead (Pb) | 2.5 – 3.7 |
| Iron (Fe) | ≤ 0.35 |
| Other Impurities | Trace |
Important: Lead exists as discrete, insoluble particles that act as chip breakers, which is the key to exceptional machinability.
Metallurgical Structure & Behavior
Phases: Alpha (α) + Beta (β)
Alpha phase: FCC (ductile)
Beta phase: BCC (stronger)
Lead distribution: Discrete globules at grain boundaries
Lead reduces tool–work friction, prevents built-up edge formation, and significantly improves surface finish.
Physical Properties
| Property | Typical Value |
|---|---|
| Density | 8.4 – 8.5 g/cm³ |
| Melting Range | 880 – 920 °C |
| Electrical Conductivity | ~26% IACS |
| Thermal Conductivity | ~115 W/m·K |
| Thermal Expansion | ~20 × 10⁻⁶ /°C |
| Color | Bright yellow |
| Magnetic Behavior | Non-magnetic |
| Corrosion Resistance | Good |
Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 300 – 500 MPa |
| Yield Strength | 100 – 350 MPa |
| Elongation | 5 – 35% |
| Hardness | 80 – 150 HB |
| Impact Toughness | Moderate |
Key Characteristics
✔ Machinability rating ~100% (industry benchmark)
✔ Excellent chip control
✔ Superior surface finish
✔ Minimal tool wear
✔ High dimensional accuracy
Available Forms
| Form | Description |
|---|---|
| Rods & Bars | CNC and automatic machining |
| Hex Bars | Screw machine components |
| Rounds & Flats | Precision parts |
| Forgings | Machined forged components |
| Extrusions | Custom profiles |
Applications
Precision screws, nuts, bolts, bushings, and spacers
Valve stems, seats, and fittings
Electrical connectors and terminals
Plumbing fittings (non-potable)
Automotive and hydraulic components
Advantages
✔ Best machinability among copper alloys
✔ Faster production cycles
✔ Reduced tooling costs
✔ Tight tolerance capability
✔ Highly recyclable
Why Choose Free Machining Brass?
Free machining brass is the industry standard for high-volume precision machining, delivering unmatched productivity, excellent surface quality, and the lowest cost per machined component.
Note: Due to lead content, it is not suitable for potable water or food-contact applications.