I cut up a trashcan full of cardboard into small pieces just to see what happened. It did get a little dull, but it took an ungodly amount of cutting to do it. I decided to move the edge to 20 degrees. That is not easy even with a 12x2.5 inch diamond stone. It is most assuredly hard and very tough. From what little I have done with it the steel looks like it will handle 20 degrees without blinking.
Are you saying the "trashcan full of cardboard" was with the edge as received? If so, what was it before you re-profiled to the 20*?