Poison it!

Any number of things will caseharden low-carbon steel and iron, burned leather, peach-pit charcoal, bone charcoal and sodium ferrocyanide are just a few. I believe the last one is the major component of "Kasenit" and has been for ages. See:

As to effectiveness, this depends on how the hardening is being done and to what. Heating up the part with a propane torch, rolling it in the compound and dunking it in a bucket of water is going to give a pretty thin hardened surface. Burying the part in a metal box of the stuff and cooking it in a furnace for awhile will give a lot deeper case. You can do the same with just about any carbonaceous material and low-carbon steel or iron. Results will vary, though.

Stan