Yes, they are hard and as Don said thin, so easily dented. If dented badly enough they will crack because they are hard enough. I wish I could touch them up, but I have tried every cold bluing solution around from .44-40, Oxpho Blue, Birchwood Casey's, etc., and none of them would do anything near the dark black finish needed to match original Weaver steel tubes.
I've got a few on my work bench right now that were painted satin black by someone who gave up on trying to blue them. I'm getting ready to strip, polish and rust blue them soon.