Introduction
This article provides a guide to 360 brass, covering composition, machinability and applications. Free-cutting brass, principally C36000 and C38500, contains a deliberate lead addition that breaks the chips during machining. It is the most widely machined brass, used for screw machine parts, fittings, valve components, fasteners and precision turned parts.
Composition
C36000 free-cutting brass contains 60.0 to 63.0 percent copper and 2.5 to 3.7 percent lead with the balance zinc, while C38500 carries 57.0 to 59.0 percent copper and 2.5 to 3.5 percent lead. The lead exists as fine particles that act as chip breakers and lubricants at the cutting edge, giving short chips, low tool wear and excellent surface finish at high spindle speeds.
Machinability and Properties
Free-cutting brass is rated near the top of the machinability scale for copper alloys, and it produces accurate, repeatable parts on automatic screw machines. Tensile strength is about 340 to 470 MPa depending on temper, and the alloy can be plated, soldered and brazed without difficulty. Its corrosion resistance is adequate for indoor and mildly corrosive service.
| Property | C36000 | C38500 |
|---|---|---|
| Copper | 60.0 - 63.0% | 57.0 - 59.0% |
| Lead | 2.5 - 3.7% | 2.5 - 3.5% |
| Machinability | Excellent | Excellent |
| Typical form | Rod and bar | Rod, shapes, forgings |
Applications
Typical products are fittings, pipe fittings, valve stems and bodies, terminals, fasteners, gears, pinions, watch and instrument parts, and plumbing components. The material is available as rod, bar and shapes under ASTM B16 and B453, and it can be supplied free-cutting to close dimensional tolerances.
Selection and Verification
Specify the temper, diameter and tolerance against the standard, and confirm the lead and copper content on the mill certificate. For parts that will be hot-formed before machining, confirm the hot-working temperature range with the supplier.
