Pretty nice little gadgeteering.
When I worked for GM, they used to use induction heating to heat treat and harden the faces of swash plates for a/c compressors. There was a nice little rig that would heat a half dozen plates to dull red in about 30s, then would automatically pop them loose into a water bath to cool. One operator would snap the plates in for treatment, then would pull them out of the bath into a bucket for the next step
Propane’s cheap. Propane forges are cheap if you build them yourself. If you’re crafty (which you hopefully are if you’re messing with a forge), then it’s easy to build your own burners with some pretty commonly available parts.
I helped a bunch of guys build propane forges built on one or two venturi burners, and am jonesing to build myself a new forced air forge (but the kid wants a playhouse, so guess what’s being built?).
Hit me up off list if you want my stash of info on burners.