Abstract: A process for case hardening steel is described. A fused bath of inert salt is maintained which bath is comprised of alkali or alkali earth halides, and alkali, or alkaline earth oxides or carbonates. To this fused bath is added urea, dicyanodiamide or pyrolysis/condensation products of urea or dicyanodiamide. This will form active ions containing carbon and/or nitrogen, and either the nitrogen and/or carbon will diffuse into the surface of a steel piece suspended in the bath to form either a nitride, carbonitride or carburized case depending upon the temperature of the bath, which is maintained between above 540.degree. C. and about 950.degree. C.