Carbon fiber in electrical contact with steel will cause corrosion of the steel if there is also a conductive path through electrolyte. Some resins will also degrade when exposed to hyrdoxyl ions generated by galvanic corrosion of metal. This causes more surface area of carbon fiber to be exposed and accelerates corrosion. Polyimides and cyanates degrade. PEEK would not degrade.
Keeping carbon fiber electrically insulated from metals is standard practice and completely prevents galvanic corrosion.
For non-corrosion resisting steels it is as Compositepro says.
Good stainless steels such as 300-series, 200-series and A-286, etc., are pretty compatible with carbon without insulation. Same goes for other good corrosion resisting materials, such as titanium and nickel alloys.
The PEEK is completely inert for all metals that I know of. The risk is galvanic corrosion from any exposed carbon.
In lower alloy SS grades (3xx) I have seen some localized corrosion issues. It really depends on how the parts were molded. There should be no exposed C Fiber at the surface.
It was fairly high chloride, sorry that I don't recall the numbers. There was pitting of the surface, not total destruction. Nearby joints that did not use filled materials did not show pitting, just etching.
Thanks for the feedback everyone. I suspected there could be issues with Carbon reinforced PEEK and steels, as I had seen problem in past when coupled with Aluminum. It is a great material just have to be careful in the application.
I've seen issues with 50% CF reinforced polymers. We solved the problem by spraying metal contact surfaces with air curing solid film lubricant (Sandstrom 27A). I think they have moved to 28A due to VOC regulations.
