Wow! It does look like someone tack welded it - the idiot!
If so, you may have to use a very sharp chisel and shatter it more, taking it off a piece at a time. Be careful not to mar the crankshaft surface.
That part of the damper is cast, so it will shatter with the right whack.
If you can get a puller to grab it, try heating the piece before trying to pull it.
Or - you could weld a hunk of steel on the remains and grab onto that.
The tack weld - try to remove as much as you can with a dremel.
After it's off - use fine Emory cloth to restore the marks.
It won't be easy, but it's still easier than putting in a new crank.
Let us know how it turns out!