Thanks also Steve. Good stuff.

I wonder if the lab did find graphite inclusions in the barrel, that it made for a higher carbon content, but the carbon available to form steel might be closer to that 1018 that you looked at. Possibly not a true medium to high carbon steel component of the damascus.

It seems like the materials used were known to have flaws, so I wonder the repeated drawing, twisting and welding was to minimize the dimension of inclusion and disperse them. In Doc Drew's micrograph, if those are carbon inclusions, they seem to be of a generally small size and separated from each other. There doesn't seem to be any obvious clusters of graphite or even larger inclusions like shown in your wrought picture.