C18200 is chromium copper, an age-hardenable alloy that trades a small amount of copper's exceptional electrical and thermal conductivity for a significant gain in mechanical strength. The composition is dominated by copper — typically 98.7% minimum — with a small chromium addition, usually in the 0.6-1.2% range, and only trace amounts of other elements. That chromium is the whole story: solution-treated and then aged, it precipitates out as fine chromium particles that pin the copper grain structure and roughly double the material's strength and hardness compared to pure copper, while conductivity stays remarkably high, typically 80% or more of pure copper (IACS).

That combination of high conductivity and real mechanical strength is why C18200 shows up in demanding electrical and thermal applications where pure copper would be too soft: resistance welding electrodes and electrode holders, spot-welding wheels, high-strength electrical connectors and terminals, and molds or components that need to conduct heat quickly while also standing up to repeated mechanical or thermal cycling. It's a specialty alloy, chosen specifically because ordinary copper alone can't survive the mechanical demands of the application.

C18200 is a genuinely different machining problem than the leaded brasses and bronzes elsewhere in this library, because it contains no lead at all. Without soft inclusions to shear the chip ahead of the tool, the material deforms plastically like a tough, gummy metal, producing long, stringy, continuous chips that want to wrap around the tool or the workpiece rather than break cleanly. Cutting forces are noticeably higher than in leaded copper alloys, and there's a real risk of built-up edge, where softened material adheres to the rake face and re-welds itself to the cutting edge, degrading finish and accelerating wear.

Age-hardened C18200 (the condition it's normally supplied and used in) is harder and somewhat more abrasive than annealed copper, but the underlying gumminess doesn't go away — it still wants to smear rather than shear cleanly. The practical fix is a sharp, positive-rake cutting edge with an aggressive chipbreaker geometry, adequate coolant to control heat and flush chips, and feed rates high enough to keep the tool cutting rather than rubbing, since light finishing passes tend to burnish the surface and work-harden it rather than cut it cleanly.

On the copper-alloy machinability scale where C36000 free-cutting brass sits at 100%, chromium copper rates dramatically lower — commonly cited in the 20% range — because it has none of the lead-driven chip-breaking mechanism that makes brasses and leaded bronzes so easy to cut. Expect noticeably lower speeds, more attention to chip evacuation, and more conservative feeds than any other alloy in this copper-alloy series.