Kasenit originally used Potassium Ferrocyanide, but I think they changed the formula before they quit making it. But any of the surface hardening compounds are just that. They are not a good substitute for the pack case hardening that can take several hours to get even 1/64" deep. There is no appreciable diffusion of carbon more than a thousandth or two deep from a quick case hardening process. There are a number of different ways to add carbon to the surface of milder steel including heating in an acetylene rich, or carburizing flame before quenching. I've made some emergency thread chasing taps or dies by putting a nut on a bolt and drilling some longitudinal holes through the thread juncture 60 or 90 degrees apart to create flutes. Then I unscrewed them and heated the nut or bolt red hot and dipped it in sugar. Then I heated it cherry red again and quenched. The sugar contains a lot of carbon, and hardens the surface enough to chase some damaged threads. Better than nothing in a pinch, but no substitute for a properly hardened tap or die made of good tool steel. I'm still hoarding my partial can of the old Kasenit too.
