Chromium copper is one of the very few copper alloys that is genuinely heat treatable, and that is the entire reason it exists. Every grade on our commercially pure copper hub — C10100 through C19400 — takes its strength from cold work alone and softens permanently if heated. Chromium dissolves in copper when hot and barely at all when cold, so C18200 can be solution treated, quenched and aged to precipitate the chromium as a fine dispersion. The result is roughly 480–590 MPa with 80% IACS conductivity retained, plus real resistance to thermal softening — which is why C18200 is the standard RWMA Class 2 resistance welding electrode material. Exotic Alloy supplies chromium copper fasteners, electrodes and machined components in the temper you specify.
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On a pure copper the temper code records only how much cold work was applied. On a precipitation-hardening copper it records a thermal history as well, and strength depends on both. TB00 is solution heat treated — the soft, supersaturated condition at about 234 MPa, used for forming. TD00 and TD04 add cold work with the chromium still in solution. TF00 is precipitation hardened straight from solution treatment. TH01 and TH04 are cold worked and then aged, stacking both mechanisms for the highest properties in the alloy — up to 593 MPa at TH04 in small section.
Section size matters far more here than on a pure copper, because the quench after solution treatment must be fast enough through the whole section to hold the chromium in supersaturation. CDA's own data show TF00 rod falling from 496 MPa at 25 mm to 379 MPa at 100 mm for exactly that reason. Do not assume thin-section properties carry into a heavy bar.
Over-ageing is the failure mode to design against. Holding the alloy above its ageing temperature — in a welding cycle, a brazing operation or in service — coarsens the precipitate and softens the material permanently. The part does not recover on cooling, and only a full re-solution-treat, quench and re-age will restore it. A welded C18200 assembly should therefore be re-heat-treated, or designed on the softened heat-affected-zone properties. Note too that CDA rate oxyacetylene welding, coated metal arc welding, spot welding and seam welding all Not Recommended on this alloy — the conductivity that makes it the premier resistance welding electrode is the same conductivity that makes it a poor candidate for being resistance welded itself.
Read the softening temperature carefully, because sources measure different things. CDA give C18200 as stable up to 371 °C (700 °F). Supplier datasheets commonly quote up to about 450 °C without significant softening, and some cite a static softening point above 500 °C. Those higher figures are static coupon values. Under sustained load with thermal cycling — the real duty of an electrode or a bolted current-carrying joint — stress relaxation begins well below them, and designing around 350–400 °C is the conservative basis.
C18200 is not covered by the ASTM nonferrous fastener standards. ASTM F468 and F467 carry a long list of copper materials — C11000, C26000, C27000, C46200, C46400, C51000, C61300, C61400, C63000, C64200, C65100, C65500, C66100, C67500, C71000 and C71500 — but chromium copper is not among them. Fasteners in C18200 are manufactured to the applicable product specification with thread conformance to the relevant ASME or ISO standard. Where a certified copper bolt to F468 is the requirement, C11000 is the listed high-conductivity choice. Standard copper cautions also apply: C18200 is galvanically noble and will drive corrosion of steel, aluminium or galvanised assemblies unless isolated, and like all coppers it is subject to stress-corrosion cracking in ammonia and amines.
C18200 carries the same CDA machinability rating of 20 as the plain high-conductivity coppers — the chromium adds strength but does not break the chip, so the alloy keeps copper's gummy behaviour, with long swarf, built-up edge and a tendency to tear. Sharp high-rake tooling, high surface speed with a light feed and copious lubricant are all needed, and in practice machining is done in the harder TD or TH tempers, which cut noticeably better than the soft solution-treated condition. Forming runs the other way: cold working is rated Excellent and the forgeability rating is 80 against 65 for the pure coppers, which is why C18200 is a standard forging and cold-heading alloy. Severe forming is done at TB00 and the part aged afterwards. Hot working is carried out at 815–925 °C.
C18200 compared with the commercially pure coppers Exotic Alloy also supplies. All data from the Copper Development Association alloy records.
| Grade | Type | Key Addition | Heat Treatable | Conductivity | Strength Range | Softening Resistance | Chosen For |
|---|---|---|---|---|---|---|---|
| C18200 | Chromium copper | 0.6–1.2% Cr | Yes — precipitation | 80% IACS | 234–593 MPa | Excellent — RWMA Class 2 | Electrodes; hot current-carrying joints |
| C10100 | Oxygen-free electronic | None — 99.99% Cu | No | 101% IACS min | 221–393 MPa | Poor | Electronic purity, vacuum service |
| C11000 | Electrolytic tough pitch | None — 99.90% Cu | No | 100% IACS min | 221–393 MPa | Poor | General electrical; ASTM F468 bolts |
| C12200 | Phosphorus-deoxidized | 0.015–0.040% P | No | 85% IACS | 221–393 MPa | Poor | Best weldability; plumbing and HVAC |
| C14500 | Tellurium copper | 0.40–0.7% Te | No | 93% IACS | 221–386 MPa | Poor | Free machining — rating 85 |
| C19400 | Copper-iron | 2.1–2.6% Fe | No | 65% IACS | 310–552 MPa | Good | Lead frames, spring contacts |
The table shows why chromium copper has no substitute among the pure coppers. Across the whole commercially pure range, strength comes only from cold work — the best any of them manages is about 390 MPa, and every one of them softens permanently if heated. C18200 breaks that trade-off by being heat treatable, reaching 480–590 MPa in the common TF00 and TH tempers while holding 80% IACS, and keeping that strength at temperature. The reason precipitated chromium costs so little conductivity is that elements dissolved in copper scatter conduction electrons badly while discrete precipitate particles largely do not — it is why 0.015–0.040% phosphorus in solution costs C12200 fifteen points of IACS, while 0.6–1.2% chromium out of solution costs C18200 only twenty. The closest pure-copper alternative is C19400, whose iron-phosphide dispersion also resists stress relaxation, but it reaches 552 MPa at only 65% IACS and is a strip product rather than a bar and forging alloy. Where higher strength is needed in a conductive copper, beryllium copper is the next step, at a further cost in conductivity.
We are committed to delivering zero-defect chromium copper fasteners and electrodes. All products undergo rigorous testing including PMI (Positive Material Identification), electrical conductivity testing to ASTM B193, hardness and tensile verification against the specified temper and section, dimensional inspection and full traceability with EN 10204 3.1 certification. Because both temper and section govern properties in a precipitation-hardening copper, every certificate states them explicitly.
Exotic Alloy exports chromium copper fasteners, electrodes and machined components to resistance welding, switchgear, power transmission, automotive and electrical equipment clients worldwide. Our dedicated logistics team ensures secure export packaging and timely deliveries by sea and air freight with full customs documentation support.