C172 Beryllium Copper
Also: C17200, CDA 172, UNS C17200, Alloy 25, beryllium copper, BeCu, copper beryllium, CuBe2, CW101C, 2.1247, Berylco 25, RWMA Class 4, C17300 (leaded free-machining version, Alloy M25), C17510 (high-conductivity beryllium copper, RWMA Class 3)
C172 beryllium copper ages to 36-42 HRC with useful conductivity: springs, contacts, bushings, spark-resistant tools. Its dust is toxic. Values TF00.
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At a glance
| Density | 8.25 g/cm³ (0.298 lb/in³) |
|---|---|
| Tensile strength | 1140-1380 MPa (165-200 ksi) typical TF00 rod; TH04 about 1210-1450 MPa (175-210 ksi); solution annealed TB00 about 410-590 MPa (60-85 ksi) |
| Yield strength | 1000-1210 MPa (145-175 ksi) typical TF00 at 0.2% offset; TH04 about 1100-1340 MPa (160-195 ksi); TB00 about 140-240 MPa (20-35 ksi) |
| Hardness | 36-42 HRC typical TF00; TH04 38-44 HRC; TB00 about 45-85 HRB |
| Elongation | 3-10% TF00; TH04 2-5%; TB00 35-60% |
| Modulus of elasticity | 128 GPa (18.5 Msi) |
| Thermal | Melts at 865-980 °C (1590-1800 °F); thermal conductivity ~105-130 W/m·K aged; electrical conductivity about 22-25% IACS aged, about 15-19% solution annealed; expansion ~17.5 um/m·K |
| Composition | 1.80-2.00% Be, 0.20% min Co + Ni, 0.6% max Co + Ni + Fe, balance Cu |
Typical values, TF00 (solution annealed and age hardened, formerly AT) rod, 25 mm (1") diameter; TH04 (formerly HT) and TB00 (formerly A) figures as noted. Confirm against the mill certificate and the purchase spec.
- MachinabilityGood
- Aged TF00 and TH04 bar cuts cleanly with carbide at moderate speed, much like a pre-hardened alloy steel, with good finishes; the soft TB00 and TD04 tempers are gummy (about 20% of C360). Use flood coolant, never cut dry or blow chips off with compressed air, and collect chips separately for return to the supplier. Leaded C17300 is the free-machining version.
- WeldabilityPoor
- TIG, electron-beam, laser and resistance welding are all possible, but the heat anneals away the aged strength and welding makes beryllium fume that needs local exhaust and exposure control; few job shops do it. Soft soldering and silver brazing with a flux made for beryllium copper are the usual joins, brazing before the age cycle.
- FormabilityGood
- Solution-annealed TB00 and quarter-hard strip form to tight radii and are then aged, which is how springs and contacts are made. Mill-hardened strip takes moderate bends as bought. Aged TF00 and TH04 bar barely bends.
- Corrosion resistanceGood
- Similar to copper: good in atmosphere, fresh water and seawater, where it also resists biofouling. Attacked by ammonia, oxidizing acids and wet sulfur compounds, and tarnishes. Non-magnetic and spark-resistant, which often matters as much as corrosion in oilfield and hazardous-area service.
C172 is copper with about 2% beryllium and a small cobalt and nickel addition, the strongest of the copper alloys. The mill solution anneals it, which leaves it soft and formable; a low-temperature age of 2-3 hours at about 315 °C (600 °F) then precipitates beryllium-rich particles and raises the tensile strength to 1,100-1,400 MPa (165-210 ksi), alloy-steel territory. It keeps about 22% IACS conductivity, is non-magnetic, resists sparking on impact, and has excellent fatigue strength and resistance to stress relaxation. Springs, connector contacts and sockets, bellows and diaphragms, aircraft landing-gear bushings, downhole oil-tool parts, spark-resistant tools, resistance-welding electrodes and plastic-mold cores and inserts are made from it.
Most machine shops buy it already aged, TF00 (solution annealed and aged) or TH04 (cold worked and aged) rod at 36-44 HRC, and machine it hard with carbide; no heat treatment follows. Formed parts go the other way: strip is stamped or formed in the soft TB00 or a quarter-hard temper and aged afterwards, or bought mill hardened and formed as is. Aging is gentle and distorts little, but the part shrinks slightly, so features that must hold close tolerances are finished after aging.
The caution is beryllium. Solid beryllium copper is safe to handle, but inhaled particles (dust, fume and mist from grinding, abrasive cutting, sanding, polishing, dry machining, welding, EDM sludge and heat-treat scale) can cause beryllium sensitization and chronic beryllium disease, a serious and incurable lung condition, and beryllium is classed as a human carcinogen. In the U.S., OSHA 29 CFR 1910.1024 sets an 8-hour exposure limit of 0.2 micrograms per cubic meter and requires exposure assessment and controls. Name the alloy on the RFQ: many shops machine it routinely with flood coolant and local exhaust, and some will not take it. Where beryllium is not acceptable, Cu-Ni-Sn spinodal alloy C72900, chromium zirconium copper C18150, or 17-4 PH stainless (without the conductivity) are the usual substitutes.
Heat treatment
Precipitation (age) hardening, in two steps. The mill solution anneals at 760-800 °C (1400-1475 °F) and water quenches (TB00), and may then cold work the material (TD01-TD04). Aging at 315-330 °C (600-625 °F), about 3 hours for TB00 and about 2 hours for cold-worked material, gives TF00 and TH04. Aging hotter (overaging, around 370 °C / 700 °F and above) trades strength for conductivity and ductility. The part shrinks slightly as it ages, so tight features are finished afterwards. Age in a protective atmosphere or vacuum, or remove the beryllium-bearing oxide by pickling, never by dry abrasive blasting.
Tempers and conditions
- TB00 (solution annealed, formerly A)
- TD01-TD04 (solution annealed and cold worked, 1/4 H to H)
- TF00 (solution annealed and aged, formerly AT)
- TH01-TH04 (cold worked and aged, 1/4 HT to HT)
- TM00-TM08 (mill hardened strip)
Stock forms
- Round, square and hex rod and bar
- Plate, sheet and strip
- Mill-hardened strip in coil
- Spring and contact wire
- Tube
- Forgings and extrusions for large bushings and tool bodies
Relative cost
Tier 5 of 5. Roughly 6-10x C360 brass per pound, the costliest copper alloy on the roster, and odd sizes carry mill lead times. Shops add for exposure control and waste handling. The premium buys steel-like strength with copper conductivity and no magnetism.
Typical applications
- Springs, spring contacts and connector sockets
- Bellows, diaphragms and pressure-sensing elements
- Aircraft landing-gear and airframe bushings and bearings
- Spark-resistant hand tools for hazardous locations
- Plastic injection-mold cores, inserts and hot-runner parts, where heat must leave fast
- Downhole oil and gas tool parts that must be strong and non-magnetic
- Resistance-welding electrodes, holders and fixtures (RWMA Class 4)
- Instrument, switch and fastener parts
Process compatibility
How C172 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | GoodGood | Aged TF00 and TH04 bar machines like pre-hard steel with carbide; flood coolant, no dry cutting, chips collected and labeled. Say "beryllium copper" on the RFQ. |
| CNC Turning | GoodGood | Bushings, pins and contacts from aged rod, held to the aged size so no heat treatment follows. |
| Swiss Machining | GoodGood | Pins, sockets and contacts from small-diameter rod; connector shops run it in dedicated, ventilated cells. |
| Metal Stamping | ExcellentExcellent | Contacts and springs from TB00 or quarter-hard strip, then aged; or from mill-hardened strip with no shop heat treatment. |
| Progressive Die Stamping | ExcellentExcellent | Connector terminals and spring fingers from coil at high rates; call the temper and the bend orientation to the rolling direction. |
| Heat Treating | ExcellentExcellent | Age hardening at 315-330 °C (600-625 °F) for 2-3 hours after forming or machining; low temperature, little distortion, slight shrinkage. |
| Vacuum Heat Treating | GoodGood | Aging in vacuum or inert gas keeps finished precision parts bright and avoids beryllium-bearing scale that would need pickling. |
| Wire EDM | GoodGood | Cuts aged material accurately with no cutting force; the dielectric sludge and filters contain beryllium and are handled as hazardous waste. |
| CNC Grinding | FairFair | Grinds well to close size, but makes fine beryllium particles: wet grinding only, with local exhaust and controlled swarf. Many shops decline it. |
| Plating | ExcellentExcellent | Gold over nickel for contacts, tin and silver for connectors, nickel for wear; plates readily once the aging oxide is pickled off. |
| Welding | PoorPoor | Anneals away the aged strength and makes beryllium fume; solder or silver braze instead, or design a mechanical joint. |
| Laser Cutting | Not recommendedNot recommended | Vaporizes beryllium into respirable fume. Profile strip by stamping or wire EDM instead. |
| Bead Blasting | Not recommendedNot recommended | Dry abrasive blasting throws beryllium-bearing dust. Remove scale by pickling and finish with wet or vibratory processes. |
Design and sourcing tips
- Call out "C17200 per ASTM B196, TF00" (or TH04) on the drawing, and say whether the part is supplied aged or is to be aged after machining or forming.
- Name "beryllium copper" in plain words on the RFQ so the shop can confirm it has exposure controls before it quotes.
- For machined parts in small quantities, buy aged TF00 or TH04 bar and skip shop heat treatment; for springs and contacts, form TB00 or quarter-hard strip and age afterwards.
- Allow for the slight shrinkage in aging, or finish critical features after aging.
- Avoid finish requirements that force dust-making operations (dry grinding, abrasive blasting, sanding, laser cutting); specify finishes that turning, milling or wet grinding can reach.
- If the program bans beryllium, look at C72900 spinodal alloy or C18150 chromium zirconium copper; for more conductivity at lower strength, C17510 runs at roughly 45-60% IACS.
Frequently asked questions
- Is beryllium copper dangerous to machine?
- Solid beryllium copper is safe to handle. The hazard is breathing fine particles: dust, fume or mist from grinding, abrasive cutting, sanding, polishing, dry machining, EDM sludge, welding and heat-treat scale. In sensitized people that can cause chronic beryllium disease, a serious, incurable lung condition. OSHA 29 CFR 1910.1024 sets an 8-hour limit of 0.2 micrograms per cubic meter. Shops machine it safely with flood coolant, local exhaust at the source, HEPA vacuums instead of compressed air, wet cleaning and separate, labeled chip collection, following the supplier Safety Data Sheet.
- What is the difference between TF00 and TH04 beryllium copper?
- Both are age hardened. TF00 (formerly AT) is solution annealed and then aged: about 1140-1380 MPa (165-200 ksi) tensile and 36-42 HRC, with more ductility. TH04 (formerly HT) is cold worked to full hard before aging, which adds strength and hardness, about 1210-1450 MPa (175-210 ksi) and 38-44 HRC, at lower elongation. TH04 bar is usually stocked only in smaller diameters.
- Is beryllium copper magnetic?
- No. C172 is essentially non-magnetic in every temper, which is why it is used for downhole measurement-while-drilling tools, instrument parts near sensors and magnets, and tools used around strong magnetic fields.
- Is beryllium copper non-sparking?
- It is, with aluminum bronze, the standard material for spark-resistant hand tools, because impact sparks from it are small and cool compared with steel. "Non-sparking" is a practical term, not a guarantee: a tool can pick up steel or rust particles that do spark, so these tools are still used with good housekeeping in flammable atmospheres.
- How hard is beryllium copper?
- Aged C172 rod runs 36-42 HRC in TF00 and 38-44 HRC in TH04, the hardest of the common copper alloys and comparable to a quenched and tempered alloy steel. Solution-annealed TB00 is soft, about 45-85 HRB, and mill-hardened strip falls in between by temper.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B196, ASTM B194 and ASTM B197
- Copper Development Association (CDA) alloy data for C17200
- Producer data sheets and safety guidance for Alloy 25 beryllium copper (Materion, NGK Berylco)
- OSHA 29 CFR 1910.1024 (beryllium standard) and the supplier Safety Data Sheet
