I recently made a set of 45 degree cut off dies for my guillotine. I thought mild steel would hold up fine for hot work. But no, they only lasted though a few cuts before dulling. I then quenched them in icy water. They have been holding up fine since. If I had to make another set I think I would use medium or high carbon steel and heat treat properly.
Fullering dies made of mild steel will probably hold up fine especially if they were ice water/brine quenched.
I do like the idea of TIG welding on a layer of stainless. It might be worth a try.
Dan