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I recently picked up my first carbon fiber bike which has a carbon fiber seat post that seized to the frame due to rust. I did not initially think that was possible but after looking at it, I believe there's more to this than meets the eye.

When taking a magnet to the frame I can see that there IS steel in the seat tube so is it the case that a carbon fiber seat post and/or a carbon fiber frame can have steel sleeves? The bike is a (2001?) Kestrel 200SCI. I want to understand the components at play here so I can safely work on unseizing the seat.

You can see how far down the steel goes by the placement of the circular magnet on the frame in the picture.

(Please note, I did not take a hammer to the seat post, that was the previous owner - thankfully the frame remained intact)

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    Looks like you've got a battle on your hands - can you get the seatpost clamp to lift up at all and see what's underneath? I'm guessing the steel clamp has dropped rust causing the steel liner tube inside the frame to rust up and lock down on the seatpost.
    – Criggie ♦
    Commented Jun 3, 2020 at 5:39
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    According to mbr.co.uk/reviews/products/token-pyrotec-seatpost-29-99 that seatpost was new to market in 2008, suggesting its not original. So there's a chance its oversized for the frame. Also it gets poor reviews, so I'd plan to try save the frame and not the seatpost.
    – Criggie ♦
    Commented Jun 3, 2020 at 5:42
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    Actually, that’s a Kestrel, and it has to be carbon. They were one of the earlier major production carbon bike makers. If the seat tube does have a steel liner, this would be a case of galvanic corrosion. Same with an aluminum liner.
    – Weiwen Ng
    Commented Jun 3, 2020 at 8:52
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    I suspect that clamp has swollen by how rusted it looks, and that could be culprit. The frame is absolutely carbon, not sure what the post is but its going to to be junk after you get it out of the frame.There's no harm in using a little bit of lube to help free it up. My advice is to pull and twist as hard as you have to, but don't apply any lateral stress to the frame. Kill the post but don't harm that frame.
    – bradly
    Commented Jun 3, 2020 at 13:44
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    Valid point about the clamp, that would be nice if it was the case. I am leaning towards using penetrating oil for a few days and trying to twist it off, if I cannot get that - I will cut the clamp off and then lastly go for cutting out the post.
    – S1r-Lanzelot
    Commented Jun 3, 2020 at 14:09

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