From: colorFabb.com

A special point of attention is the abrasive nature of the carbon fibers. In general these fibers will accelerate the nozzle-wear of brass nozzles, much faster than unfilled filaments. Therefore we  recommend to use nozzle’s from Stainless steel or hardened copper alloys.

While it's tempting to try using filament containing carbon fiber, many users are reporting trouble extruding after using that material, even from different vendors. We've seen people that wear out the inside of their nozzle, not to mention having lingering extrusion issues after switching to more common filament types. One of the benefits of carbon fiber containing materials are it's strength, similarly to good quality plywood. The interlocking long carbon fiber strands give the material a super-strong core. All the filaments we've seen so far however, don't have that same kind of long carbon fiber strands, so your prints are similar to Oriented Strand Board (cheaper plywood with smaller fiber length), which isn't as strong or as durable. That somewhat defeats the purpose of using carbon fiber materials. We find that for applications needing high-strength printed parts Nylon is a great material. While a bit slower to print, the parts are much, much stronger.