Hardened metal and home shops.

[Hawkeye]

I don't have a good feel for the numbers, but if a regular file won't cut a piece of metal, I'm not cutting it.

If you have the heat available to anneal the piece, you should be able to harden and temper it. The methods would be more traditional, watching colours and such. Might be worth researching heat treating in the blacksmithing forums. I'd try it on a spare piece of the metal, or at least make sure you have enough to redo it if necessary.

Sometimes, heating the piece part way, then covering it with borax to keep the air off can prevent scaling.