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Copper Forging: C101, C110 and Tellurium Copper

Copper forges, but the reason you forge it is almost always electrical or thermal, not structural. The grades that matter are chosen for conductivity to four significant figures, and the forging process exists to put dense, void-free, high-conductivity metal into a shape that machining from rod cannot reach economically. Oxygen content, not strength, drives the grade decision.

ISO 9001ISO 14001AS9100
Copper forging grades are differentiated by how they handle oxygen, because oxygen content controls both conductivity and forgeability. C110 (ETP, electrolytic tough pitch) is the common 99.9% copper, but it contains a small amount of dissolved oxygen as cuprous oxide. That oxygen is harmless until you heat the part in a reducing or hydrogen-bearing atmosphere, at which point hydrogen diffuses in, reacts with the oxide to form steam at the grain boundaries, and embrittles the metal, the classic hydrogen embrittlement that cracks ETP copper. For hot forging in clean atmosphere it works, but it limits your options. C101 (OFHC, oxygen-free high-conductivity) removes the oxygen entirely, so it is immune to hydrogen embrittlement and is the grade you forge when the part will see brazing, welding or reducing-atmosphere heat, or when you need the highest reliability. It is the default for forged bus bars, contacts and high-current connectors in demanding applications. Both C101 and C110 deliver around 100% IACS conductivity, which is the whole reason to use them. The metallurgy point that trips people up: you do not pick copper forging grades for mechanical properties, you pick them for conductivity and atmosphere tolerance. If a buyer asks for a strong forged copper part, the honest answer is that pure copper is soft and you should be looking at a copper alloy (chromium copper, beryllium copper) or brass instead.

Hot Forging, Hot Shortness and Cold Coining

Pure copper hot forges in roughly the 1400-1650°F range and flows beautifully because it is extremely ductile. The risk is hot shortness from impurities, particularly trace lead, bismuth or sulfur, which form low-melting grain-boundary films and cause the part to crumble or crack at forging heat. This is exactly why high-purity, controlled-chemistry stock (C101/C110) is used and why scrap or uncertified copper is dangerous to forge. Because copper is so soft and ductile, much copper shaping is actually done cold or warm: cold heading, cold coining and impact extrusion produce contacts, terminals and rivets at high speed with excellent surface finish and work-hardened strength. Cold work raises hardness and tensile strength substantially but lowers conductivity slightly and the part may need a stress-relief or full anneal afterward to restore ductility and conductivity. So the process choice is really hot forge for larger near-net shapes versus cold form for small high-volume parts. Copper galls and sticks to dies as readily as it conducts, so lubrication matters, and its high thermal conductivity means a hot billet dumps heat into cold dies fast, chilling the surface. Heated dies or fast forging cycles help. The upside is that forged or cold-worked copper is fully dense with no porosity, which matters enormously for high-current and high-vacuum parts where a single void is a failure.

Where Forged Copper Is Worth the Trouble

The applications that justify forging copper rather than machining it are almost all electrical and thermal. High-current bus bars, switchgear contacts, electrode holders, welding tips, induction-heating components and waveguide parts are forged in C101 and C110 because forging delivers the full-density, high-conductivity, net-or-near-net shape that a machined-from-plate part would waste expensive copper to achieve. Tellurium copper enters here as the machinable option: a small tellurium addition gives near-free-machining behavior while keeping 90-95% IACS, so parts that are forged near-net and then heavily machined use C145 tellurium copper to keep the secondary machining cheap. Semiconductor and vacuum applications drive demand for OFHC C101 specifically, because oxygen-free copper is required for high-vacuum brazing and outgassing-sensitive components. The forging gives a homogeneous, void-free blank that brazes leak-tight. Thermal-management parts, heat sinks and high-power-electronics baseplates use forged copper where conductivity must be maximized and casting porosity would create thermal hot spots. In all of these, the value is in conductivity-per-shape, and forging is justified when the geometry plus volume make machining from solid copper wasteful, since copper stock is expensive and chips, while recyclable, represent real lost value.

Frequently Asked Questions

Both are roughly 99.9% pure copper delivering about 100% IACS electrical conductivity, but they differ in oxygen content, which drives their behavior in heated processes. C110 is ETP (electrolytic tough pitch) copper and contains a small amount of oxygen as cuprous oxide. That oxygen makes it susceptible to hydrogen embrittlement: if the part is heated in a hydrogen-bearing or reducing atmosphere, hydrogen diffuses in, reacts with the oxide to form high-pressure steam at the grain boundaries, and cracks the metal. C101 is OFHC (oxygen-free high-conductivity) copper with the oxygen removed, so it is immune to hydrogen embrittlement and is the correct choice whenever the part will be brazed, welded, or heated in a reducing atmosphere, as well as for the highest-reliability and high-vacuum applications. For hot forging done in a clean, controlled atmosphere, C110 is acceptable and slightly cheaper, but most demanding forged copper parts specify C101 to eliminate the embrittlement risk entirely. Neither is chosen for strength; both are soft, so if you need mechanical performance, look at a copper alloy instead.
Pure copper is deliberately soft and ductile, with low yield strength, because the grades used for forging (C101, C110) are optimized for electrical and thermal conductivity, not mechanical performance. Annealed copper has a tensile strength around 32 ksi and yields at well under 10 ksi, and even cold-worked it does not approach the strength of structural metals. If a part needs to carry significant mechanical load, forging pure copper is the wrong call. The honest alternatives depend on whether you still need conductivity: chromium copper (C18150) and beryllium copper (C17200) are precipitation-hardenable copper alloys that reach much higher strength while keeping 50-85% IACS conductivity, and they forge well, making them the right choice for electrodes, resistance-welding tips and high-strength contacts. If conductivity is not required, brass (C360, naval brass) or bronze gives far better strength and machinability at lower cost. Reserve pure copper forging for parts where maximum conductivity is the governing requirement and mechanical load is modest, such as bus bars and high-current connectors.
It depends on part size, volume and the strength you want. Pure copper hot forges around 1400-1650°F and flows extremely well, making hot forging the choice for larger near-net shapes such as bus bars, electrode holders and switchgear parts. The trade-off is that hot working leaves the metal soft and annealed. Because copper is so ductile, a great deal of copper shaping is instead done cold or warm: cold heading, cold coining and impact extrusion produce small high-volume parts like terminals, rivets and contacts at high speed with excellent surface finish. Cold working also work-hardens the copper, raising its hardness and tensile strength substantially, though it slightly lowers conductivity and may require a stress relief or anneal afterward to recover ductility and conductivity. So the practical guide is: cold form small, high-volume parts where the work-hardened strength is a bonus, and hot forge larger or thicker shapes. In both cases the result is fully dense, void-free metal, which is critical for high-current and high-vacuum reliability. Watch for hot shortness in hot forging if the copper has any lead or bismuth contamination.
Tellurium copper (C145) solves the machinability problem that plagues pure copper. Forged copper parts frequently need significant secondary machining to hit final tolerances on contact faces, bores and threads, but pure C101 and C110 are gummy and machine poorly, producing stringy chips, built-up edge and slow material removal. Adding about 0.5% tellurium gives copper near-free-machining behavior, similar to leaded brass, while retaining roughly 90-95% IACS conductivity, which is high enough for most electrical applications. So when a part is forged near-net and then requires heavy machining, specifying tellurium copper keeps the machining fast and cheap without sacrificing much conductivity. The tellurium forms fine particles that break chips cleanly. It forges similarly to pure copper, with the same need for clean atmosphere and care against hot shortness. The trade-off is the slight conductivity reduction and a small premium on raw material, but for any forged copper part with substantial machining content, that trade is almost always worth it. If absolute maximum conductivity is required, stay with C101 and accept the harder machining.
Copper raw material is expensive and moves with commodity copper prices, so material is a larger fraction of part cost than with steel, and minimizing scrap by forging near-net is part of the economic justification. Forging itself is not unusually difficult since copper is soft, but galling, die chilling from copper's high thermal conductivity, and the need for clean atmosphere add process care. Tooling for a closed-die copper forging runs in the same general range as other metals, roughly $10,000-$50,000 for an impression die, so volumes of several hundred to a few thousand pieces are needed to beat machining from rod or plate. Cold-formed copper parts (headed, coined, impact-extruded) carry their own tooling cost but run at very high rates once set up. Lead time from a cold start is dominated by tooling, commonly 6-12 weeks, then 2-4 weeks for the run plus any anneal and finish machining. For prototypes and low volumes, machining C110 or tellurium copper from bar is faster and avoids tooling. Forging wins where conductivity, full density and material savings at volume all point the same way.

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Last updated: July 2026

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