John Ings wrote in message . ..
"Poison it!" my machinist mentor used to say, making reference to case
hardening using compounds that used to contain cyanide among other
things.

They don't any longer I understand, but what do they contain? And are
they as effective? Does anyone know?

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:
https://www.travers.com/htdocs/msds/pdf/81-003-001.pdf

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