In this process, the casting is quenched in a salt bath or metal bath from the hardening temperature down to slightly above the martensite temperature (see Martensite point) and maintained at this temperature until reaching equilibrium temperature. Then the casting is cooled down to room temperatures using any kind of cooling process.

Additional references:
Salt bath furnace
Flame hardening
Case hardening
Electron beam hardening
Induction hardening
Laser hardening
Nitriding
Immersion hardening