Hardening and Tempering are used to provide the best combination of hardness, strength, and toughness in a steel for a given engineering purpose. This treatment consists of heating the steel above the transformation range, holding for a long enough time to insure uniform temperature and solution of the carbon and alloying elements in an austenitic microstructure, followed by rapid cooling (quenching) to a fully martensitic structure. The cooling medium can be air, oil, water, molten salt, fluidised bed, or a gas such as argon or nitrogen. Upon completion of hardening, the steel is in it’s hardest but most brittle condition. It is necessary to perform a subsequent tempering or drawing or process to produce a softer but much tougher condition.