I think what XXXXXX writes in that message, and what I have written above mean about the same thing. I put things into laymans terms and he took the technical route. THe only difference I can see would be the stretching of only the surface. If this were the case, then simply sanding the hardened, compressed surface would relieve the stresses and the rest would pop right back up into place. At least that how I understand it would be if that theory were correct. Not being a scientific kinda guy, I couldn't care less how the molecules of metal are stacked. I can't see them, so to me, they are a non-issue. As long as you can shape a piece of metal to look how you want it and it not be stressed and under tension, then you've done your job well. This is a whole other story for another day.
The question here was how to fix the stretched metal from sandblasting. It can be done effectively with a shrinking disc, but be prepared to spend several hours trying to get it right. My advice: get another set of doors.
And remember my motto "Metal is stupid. You control the metal, the metal never controls you."
Metalshaping & Kustom Paint