OK, from what Ed & Tim said, I do want something harder than mild steel, so that it won't "yield" as soon as mild steel would.
As to heat treating facilities, well, minimal - maximum heat capability is propane forge. Obviously no automatic temp control.
As to what I'm making: it's for taking down tin ceilings. The ceilings will be salvaged, so the specifics of the tool are needed to minimize damage. The bar needs to be about 16" long, to reach over the back of a
24" tile. It needs to have a long taper, coming to a thin edge, to work under the nails without distorting the tin. One edge needs to be 3/4" wide to fit into a nailing space. One end will be straight & the other have a 90 degree leg. It will be pulling out 1" long 16 ga nails, so it won't have to be very strong - I'm thinking 1/16" thick (from trials with a 1/16" thick putty knife).
If it wasn't for the length, I would re-shape the putty knife. Which suggests brazing or silver soldering the knife on a longer handle - is that doable? How about a 90 bend in it - I assume that would require heating to bend, quenching, and tempering?