If your part needs both the electrical conductivity of pure copper and the chip-breaking behavior that prevents birds-nesting around a turning tool, C14500 tellurium copper is the practical answer. It trades only 5–7% of the conductivity of electrolytic tough pitch (ETP) copper for machinability ratings in the 85–90% range — making it the go-to free-cutting copper for electrical connectors, welding torch tips, plasma-nozzle components, and high-volume turned parts where cycle time and surface finish matter as much as the material bill.
What C14500 Actually Is: Grade, Family, and Specification
C14500 is the UNS designation for tellurium-bearing free-cutting copper. It is also known as CuTeP (ISO/EN designation CW118C, though the exact EN number can vary by product form) and falls squarely in the wrought copper family — not a brass, not a bronze, not an alloy steel. The tellurium addition (0.40–0.70%) forms finely dispersed Cu₂Te particles in the copper matrix. These particles concentrate shear during cutting, causing the chip to curl tight and snap short rather than forming the long stringy ribbons that pure copper produces.
In the Chinese GB/T system there is no identical grade; T2 (Cu-ETP, UNS C11000) is the chemically closest pure copper but lacks tellurium and machines completely differently. The relevant ASTM standard is ASTM B301/B301M for free-cutting copper rod and bar. ISO equivalents are covered under ISO 1337 (wrought copper) and ISO 6957 (copper alloys).
Chemical Composition per ASTM B301
| Element | Content (wt %) | Purpose |
|---|---|---|
| Cu (incl. Ag) | 99.5 min | Base metal; provides electrical and thermal conductivity |
| Te | 0.40–0.70 | Forms Cu₂Te chip-breaking dispersoids; the defining addition |
| P | 0.004–0.012 | Deoxidizer; prevents hydrogen embrittlement during annealing |
Source: ASTM B301/B301M-13, Table 1. Trace impurities are not individually specified beyond the copper minimum.
Mechanical Properties by Temper (ASTM B301, Rod and Bar)
| Temper | Tensile Strength (MPa) | Yield Strength 0.2% offset (MPa) | Elongation in 50 mm (%) |
|---|---|---|---|
| H04 (hard) | 310 min | 276 min | ~4 |
| H02 (half-hard) | 255–310 | 205–276 | ~8 |
| H01 (quarter-hard) | 240–290 | 172–240 | ~12 |
| O61 (annealed) | 221–276 | 69–103 | ~50 |
Values per ASTM B301. Hardness in H04 temper typically 62–68 HRB; annealed stock ≤45 HRF. Actual values depend on section size, cold-work history, and test temperature.
Physical Properties at Room Temperature
- Density: 8.94 g/cm³ — essentially identical to pure copper
- Electrical conductivity: 93–95% IACS annealed; drops to ~90% IACS in H04 hard temper. C11000 ETP copper reaches ~101% IACS annealed for comparison.
- Thermal conductivity: ~370 W/(m·K) at 20°C (reduced ~5% from pure copper’s ~390 due to tellurium)
- Melting range: ~1050–1075°C
- Electrical resistivity: ~1.86 μΩ·cm (annealed); ~1.92 μΩ·cm (H04)
Corrosion and Environmental Behavior
C14500 inherits copper’s general atmospheric corrosion resistance: it forms a protective green-brown patina outdoors and resists fresh water, non-oxidizing acids, and neutral salt solutions. However, the tellurium dispersoids create micro-galvanic sites that can slightly accelerate pitting initiation in aggressive chloride environments relative to pure copper — the effect is measurable in salt-spray testing but rarely disqualifies C14500 in practice.
At elevated temperature in air, C14500 oxidizes similarly to pure copper. Above ~400°C, scaling becomes significant enough to require protective atmosphere during brazing or annealing. Tellurium does not form a protective oxide film, so high-temperature oxidation resistance is essentially that of copper.
CNC Machining: What Changes with Tellurium
Chip Formation and Tool Engagement
The Cu₂Te particles are the entire story for machining. They are hard, brittle, and insoluble in the copper matrix. As the cutting edge advances, stress concentrates at the Cu₂Te/matrix interfaces, causing the chip to fracture into short 3–8 mm needle-like segments — fundamentally different from the continuous ribbons from C11000.
This chip morphology changes how you program the machine:
- Chip evacuation is rarely a bottleneck; you can use uncoated carbide with positive rake and aggressive feed rates without chip-management dwells.
- Built-up edge (BUE) formation is suppressed compared to pure copper, because short chips spend less contact time on the rake face.
- The machinability rating of ~85% (C36000 free-cutting brass = 100%) means cycle times that would be 3–4× longer in ETP copper can come down to near-brass levels.
Starting-Point Cutting Parameters
These are starting references for C14500 H02 on a rigid CNC lathe or mill. Actual values change with machine stiffness, workpiece fixturing, tool holder overhang, coolant delivery pressure, and the specific coating/geometry of your insert.
| Operation | Cutting Speed (m/min) | Feed Rate (mm/rev) | Depth of Cut (mm) |
|---|---|---|---|
| Turning (carbide, uncoated or TiN, K10–K20) | 180–350 | 0.05–0.30 | 0.5–4.0 |
| Turning (HSS, finish passes, small diameters) | 60–120 | 0.03–0.15 | 0.2–1.0 |
| Face milling (carbide, 45° lead) | 200–400 | 0.10–0.25 mm/tooth | 0.5–3.0 |
| Drilling (carbide, 118° point) | 80–160 | 0.05–0.20 | — |
| Tapping (spiral-flute HSS, cutting oil) | 8–18 | — | — |
Tool geometry matters more than coatings here. Use inserts with sharp cutting edges (honed rather than chamfered), high positive rake angles (12–18°), and generous clearance (8–12°). TiN or TiCN coatings help reduce galling on long runs; polished uncoated carbide also works well. For small drilled holes (≤3 mm), HSS drills with polished flutes and a split point consistently outperform coated carbide in tellurium copper — coating thickness can dull the cutting lip on micro-scale geometries.
Coolant and Lubrication
C14500 machines well dry for turning if the speed-feed combination keeps the chip from re-welding. For drilling, tapping, and long production runs, use a light soluble oil (5–8% concentration) or a straight cutting oil for threading. Avoid chlorinated EP additives unless post-machining cleaning can guarantee removal — residual chlorine can initiate stress-corrosion cracking if the part sees humidity and tensile stress in service.
Heat Treatment
C14500 is not hardenable by heat treatment. Tellurium does not form coherent precipitates, and there is no quench-and-temper response. This is a common misunderstanding — CuTe does not behave like a heat-treatable steel.
What you can do:
- Annealing: 425–650°C for 30–60 minutes, air or water cool. Lower temperatures for partial anneal (stress relief), upper range for full recrystallization to O61 temper. Avoid hydrogen-bearing atmospheres — tellurium forms volatile H₂Te, which causes subsurface porosity.
- Stress relieving: 200–300°C for 1 hour. Useful after heavy cold forming or when dimensional stability is critical.
Work hardening is the only practical strengthening mechanism. Starting from annealed stock, a 30–40% cold reduction can double tensile strength while halving elongation.
Surface Finishing
C14500 accepts the same surface treatments as other coppers, with one tellurium-specific caveat: electroplating adhesion can be inconsistent if Cu₂Te particles are smeared across the surface by dull tooling. A light etch (5–10% sulfuric acid dip, 30 seconds at room temperature) removes the smeared layer and exposes clean copper.
- Electroless nickel plating: Good adhesion after acid activation; wear resistance for connector pins.
- Silver plating: RF connector bodies and bus-bar contacts.
- Tin plating: Solderable terminals.
- Passivation (benzotriazole): Short-term tarnish protection in storage.
- Chemical polishing: Achievable, but tellurium dispersoids produce a slightly matte finish — mirror polish on C14500 is softer-looking than on C11000.
Where C14500 Gets Specified
- Electrical connectors and terminals: High-volume turned pins, sockets, and bus-bar fittings where conductivity above ~90% IACS and tool life drive economics.
- Welding and plasma-cutting tips: MIG contact tips and plasma torch nozzles. Conductivity plus machinability means thread-form quality without the tearing common to pure copper.
- EDM electrodes: Sinker EDM electrodes. C14500 electrodes wear ~5–8% faster than pure copper electrodes but cost 30–50% less to machine.
- Heat sinks: Turned heat sink bases with complex milled channels. The ~370 W/(m·K) thermal conductivity is close enough to pure copper’s ~390 W/(m·K) for most thermal designs.
- Fasteners and threaded inserts: Custom copper bolts, nuts, and bushings for electrical assemblies. C14500 threads cleanly — tap cutting rather than tearing.
Comparison with Alternative Materials
| Property | C14500 (H02) | C11000 ETP Cu (H02) | C36000 Brass (H02) | C18150 CuCr1Zr |
|---|---|---|---|---|
| Electrical conductivity (% IACS) | ~93 | ~100 | ~26 | ~80 |
| Thermal conductivity (W/(m·K)) | ~370 | ~390 | ~115 | ~330 |
| Machinability rating | 85–90 | 20 | 100 | 20 |
| Tensile strength H02 (MPa) | 255–310 | 240–300 | 340–450 | 350–480 |
| Relative material cost | 1.1–1.3× C11000 | Base (1.0×) | 0.8–1.0× C11000 | 3–5× C11000 |
The decision tree: if you need conductivity above 90% IACS AND need to machine thousands of parts, C14500. If conductivity is not critical and you want maximum tool life, C36000 brass. If you need the highest conductivity regardless of machining difficulty, C11000 with patience and specialized tooling. If you need both conductivity and elevated-temperature strength, C18150 at 3–5× the cost.
C14500 is often described as “similar to C11000 but machinable.” That is correct for classification but misleading for procurement — they are not directly interchangeable. Swapping C11000 for C14500 changes the conductivity specification; swapping C14500 for C11000 changes cycle time, tool life, and per-part cost. Stick to the UNS number on your drawing.
What to Include in Your RFQ or Drawing Package
- Full material designation: UNS C14500, temper (H02, H04, etc.), product form (rod, bar, hex), and ASTM B301. “Tellurium copper” alone is not sufficient.
- Conductivity requirement: If electrically critical, state minimum % IACS at a stated temper and temperature. ASTM B301 does not mandate a conductivity minimum; heavily cold-worked stock can drop below 90% IACS.
- Surface finish: Critical surfaces and Ra targets. For plated surfaces, specify pre-plating preparation and plating thickness per the relevant ASTM standard.
- Tolerances: ISO 2768-m or -f, with direct ± values on tight features. Threads to ISO metric or UN profile with fit class.
- Quantity and delivery: Prototype vs. production volumes drive tooling strategy and fixture investment.
Data sources: ASTM B301/B301M Standard Specification for Free-Cutting Copper Rod and Bar; Copper Development Association (CDA) Standards Handbook; ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys. Machining parameters are starting references only; actual values depend on specific machine, tooling, fixture, coolant, and workpiece geometry.
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