T2 copper is the electrolytic tough pitch (ETP) pure copper grade most Chinese machine shops
quote when an engineer writes “copper, high conductivity” on a drawing. In UNS terms it is C11000;
where the part exists only to carry current or dump heat, T2 is usually correct and cheapest. It stops
being right as soon as the part must be welded, brazed in a reducing atmosphere, hydrogen-fired, or held
hot in service: the oxygen inside ETP copper as Cu2O can react and crack the part from the
inside. Confirm oxygen content and supply condition before releasing the drawing, and for exposed,
outdoor or chemical service check whether C10100 or C10200 oxygen-free copper, or a brass or bronze,
fits better.
Material identity: what T2 actually is
T2 is a Chinese national-standard designation under GB/T 5231 (Wrought copper and
copper alloy grades and chemical composition). The “T” prefix marks a pure wrought copper; T2 is Cu-ETP
and UNS C11000. Two naming traps matter. “Pure” is not 99.99%: Cu-ETP is
copper of at least 99.90% purity with oxygen deliberately left in the melt at a low, controlled level —
routine engineering copper, not laboratory-grade metal. T2 and C11000 are not one identical
document: GB/T 5231 and ASTM B152 impose different oxygen limits and property tables, so a
China-quoted T2 and a US-quoted C11000 can arrive at the same drawing without being the same material.
If conductivity demand or environment is tighter than general ETP copper supports, compare the
oxygen-free routes in our notes on C10100 oxygen-free copper and
C10200 oxygen-free copper performance; for the family’s electrical and thermal
numbers see the C11000 conductivity reference.
Chemistry, and the oxygen number that decides the part
The table below collects only the composition limits that matter to a machinist or buyer, with the
standard each comes from (limits set by the standards, not measurements of a specific heat).
| Element | Content | Standard / note |
|---|---|---|
| Cu | >= 99.90% | GB/T 5231 (T2); ASTM B152 (C11000) |
| O (oxygen) | <= 0.002% | GB/T 5231 T2 limit |
| O (oxygen) | <= 0.040% | ASTM B152 C11000 limit |
| Other elements, total | <= 0.1% | both specifications, “others” |
| Electrical conductivity | nominally ~100% IACS (101% min typical for C11000) | GB/T 5231 / ASTM B152 (IACS = International Annealed Copper Standard) |
Read those two oxygen rows together — they are the point of the grade. A GB/T 5231 T2 heat is capped
at 0.002% oxygen; an ASTM B152 C11000 heat is allowed up to 0.040%. Both are “tough pitch” copper
(oxygen as Cu2O for castability) but the Chinese limit is far tighter. T2 suits warm-forming
or light brazing better; both remain unsuitable for hydrogen-bearing atmospheres at temperature. A
specification that says “oxygen-free copper” means C10100 or C10200, not T2.
Temper and supply condition
Copper is bought by temper, and temper, not grade, sets most of the properties you measure. Common
wrought tempers are annealed (soft, O60), half-hard (H02) and hard (H04); the designation and property
table live in the standard for your product form (plate/sheet/strip under ASTM B152; wire/bar under
B187/B49). Two consequences show up immediately. Hard temper cuts better and bends worse:
cold-worked T2 is stronger with cleaner chips, but less ductile and fights a tight bend radius.
Soft temper is the machinability trap: annealed copper is gummy — it smears, builds a
rough surface and grabs a dull tool. Cold work also raises strength while lowering conductivity; a light
anneal after forming restores it. State the temper, not just the grade.
Typical mechanical and physical properties
The figures below are typical values for annealed (soft) T2 / Cu-ETP, to sanity-check a
vendor datasheet. They are not minimums and shift with temper, section size and product form; confirm
the standard edition in your contract.
| Property | Typical value (annealed) | Condition / unit / basis |
|---|---|---|
| Tensile strength, Rm | ~200-250 | annealed strip/bar, MPa |
| 0.2% proof strength, Rp0.2 | ~50-70 | annealed, MPa |
| Elongation, A | ~40-50 | annealed, % |
| Hardness | ~100-120 | annealed, HV2.5 (approximately 40-45 HRB / 35-45 HV on thin strip) |
| Electrical conductivity | ~100 (101 min for C11000) | % IACS |
| Thermal conductivity | ~390-400 | W/(m*K), room temperature |
| Density | 8.9 | g/cm3 |
Note the hardness scale: HV2.5 is a microhardness scale; its numbers are not HRB numbers even for the
same soft copper. If a customer quotes “40 HRB” and a mill cert says “40 HV2.5,” the material may be
softer or harder than expected. Always quote the scale.
Corrosion and temperature behaviour
T2 is a good general-purpose outdoor and fresh-water material: it builds a protective patina in
atmosphere, resists fresh water and neutral salts, and in medical or food-contact use copper is valued
for its antimicrobial surface action. It is not a universal chemical material.
Ammonia and ammonium compounds attack it and can cause stress-corrosion cracking in
cold-worked parts; annealing is the usual mitigation. Hydrogen and reducing atmospheres at
elevated temperature are the classic failure mode: internal Cu2O reacts with hydrogen
and the generated steam pressure cracks the metal — why oxygen-free grades exist.
Sulphide-bearing and polluted atmospheres tarnish it heavily, and copper’s high potential
makes it a strong cathode in bolted dissimilar-metal joints, so galvanic corrosion needs care. For
marine, salt-spray or chemical service, a cupronickel (C70600) or aluminium bronze is normally correct.
CNC machining T2 copper: what changes with this material
Pure copper is soft, highly thermally conductive and chemically “sticky” against tool material —
three facts that drive every practical decision.
- The workpiece absorbs heat, not the chip. Copper conducts heat away so well that
the tip may stay cool while the part grows warm and expands; over a long batch that can move a
“perfect” dimension out of tolerance. Finish tight features last. - Build-up edge and smearing are the default failure mode. Soft copper welds to the
edge and tears off, giving rough surfaces and unstable size. A sharp positive-rake edge and cutting oil
usually beat raw speed. - Hard temper helps if the feature allows it: half-hard or hard stock cuts cleaner
and stiffer. - Deep holes and thin walls move; chips tangle. Low proof strength lets walls deflect,
so support them and take lighter depths.
Starting tool and parameter guidance (conditional)
The table below is a starting point only. Actual results depend on machine rigidity,
tool grade and coating, edge preparation, coolant, workholding, and the temper and purity of the heat —
dial-in starting values, not a recipe, with no promise of achievable roughness or tolerance.
| Operation | Cutting speed | Feed | Depth of cut | Notes |
|---|---|---|---|---|
| Turning (soft temper) | 150-300 m/min | 0.05-0.2 mm/rev | 0.3-2 mm | Sharp positive-rake PVD insert; neat or high-pressure oil |
| Turning (half-hard / hard) | 200-400 m/min | 0.05-0.25 mm/rev | 0.3-3 mm | Cleaner chips; PCD or polished carbide |
| Milling | 120-300 m/min | 0.03-0.2 mm/tooth | 0.5-3 mm | 2-3 flute polished carbide; climb cut; strong chip evacuation |
| Drilling | 60-150 m/min | 0.05-0.2 mm/rev | full dia. | Thinned-point, polished-flute drill; peck deep holes |
| Threading / tapping | 30-80 m/min | per pitch | per pitch | Form taps can seize; a cut tap with lubricant is safer |
Two reminders outrank any numbers: keep the edge sharp (replace rather than “chase” a dull
insert) and keep chips cleared (recutting a chip causes most torn finishes). See how the same
shop approaches C11000 conductivity parts.
Surface finish and finishing options
T2 takes almost any finish, and copper’s chemistry limits some of them. Native /
lacquered: polished copper looks excellent but tarnishes, so a clear protective coat is common
on visible parts. Nickel / tin / silver plating: used for solderability, wear and
appearance. Passivation: copper has no protective oxide barrier, so it will not
“passivate” in the stainless sense. Do not assume food or medical compliance: those are
regulatory determinations about the finished assembly, not a property of the grade.
Applications, and when another copper fits better
T2 earns its place wherever conductivity or heat transfer drives the design: busbars, terminals, lugs
and shunts; heat-sink bases and cold plates; EDM electrodes; RF waveguides and connectors; brazed and
soldered assemblies whose process suits ETP oxygen; and antimicrobial touch surfaces, subject to the
applicable approval regime. The table compares grades in a comparable annealed condition, since
temper changes everything; “nearly equivalent” designations are not drop-in interchangeable without
checking the standard edition in your contract.
| Grade | Family | Key character | Choose it when |
|---|---|---|---|
| T2 / C11000 | ETP pure copper | ~100% IACS, good formability, contains O | General high-conductivity parts where cost matters |
| C10100 | Oxygen-free (OFE) | Cu >= 99.99%, O extremely low | Top conductivity plus oxygen-free duty |
| C10200 | Oxygen-free (OF) | Cu >= 99.95%, O very low | Oxygen-free duty where 99.99% purity is unneeded |
| C14500 | Tellurium copper | Free-machining copper, still conductive | High-production turning where T2 smears |
| C17200 | Beryllium copper | Spring/high-strength copper, precipitation hardened | Contact springs and high-strength conductive parts |
| C70600 | Cupronickel 90/10 | Seawater corrosion resistance | Marine / salt-water service, where pure copper is wrong |
What to put on the drawing and in the RFQ
To get a comparable quote, send: the drawing (2D with tolerances, plus 3D if
available); the copper specification by standard edition (e.g. “T2 per GB/T 5231” or
“C11000 per ASTM B152”); the temper / supply condition (O60, H02, H04, …) and product
form; the quantity and any traceability or mill-cert requirement; the critical
tolerances and datum scheme; the surface finish (Ra and type); and the
service environment (temperature, chemicals, hydrogen exposure, food or medical contact)
so the oxygen question is settled before the parts are made.
Those items avoid the two classic T2 failures — a conductivity / oxygen mismatch and a soft-temper
finish problem. Read our prototype CNC machining RFQ and validation checklist, then
send the drawing, material specification, condition, quantity, tolerances and surface requirement
through the quote request page.
Turn this machining question into a manufacturable part
Need this material or process for your next CNC project?
Send your STEP, STP, IGES, DXF, PDF, material, quantity, surface finish, and tolerance requirements. We will review manufacturability and reply with practical quotation guidance.
