If it is a case hardened frizzen and you are through the carbon layer, you can add carbon, by treating it with something like Kasenit, add a thin veneer of high carbon steel (half soling) or replace it.
Gotcha ! Half-soling will probably make it last forever. Most I have seen were high temp epoxied, but I suppose you could solder or weld it if you knew how. I like the fact that you want to fix the old one, good thinking!
"Be nice, until its time to not be nice" (Patrick Swayze...Roadhouse)
half soling isn't hard. you need a piece of very thin clock spring, or spring steel stock. 1/32 or less in thickness. (thinner the better) Using as little heat as possible cut the spring stock so it is just slightly larger than the frizzen face. Roughen the frizzen face and roughen the outside curve of the spring piece. A rubbing with a rough grind stone does a good job. Clean both pieces, epoxy the roughend surfaces and clamp together tight with a C-clamp for 24 hours. Then again, with out heat slowly grind the edgr of the spring stock back to meet the frizzen edges. I have done a few tc frizzens that way. My brother still uses one after 25 years.