Reyd

If you've got real good ventilation, you could case harden it. My
grandfather, who grew up as a blacksmith, used to do that occasionally
to carbon steel. Get some sodium cyanide pellets, put them in a sturdy
metal pan and melt them (traditionally you set them in the forge, but he
used a propane torch - melts at 568 deg. C according to my "Handbook of
Chemistry and Physics"). Stick the piece to be hardened in and let sit.
Rule of thumb is 1/32" of depth per minute (though I think it hits a
diffusion limit around 8-10 minutes). Be careful, cyanide is toxic and
molten salts are tricky to work with. My grandfather was pretty casual
about doing it, but he grew up in the era of lineshafts and expendable
oil punks (the kids that crawled around in the rafters and oiled the
bearings while things were running - if they got tangled up in the
belts, you just got another one).

Jim