The steel is hardened through a special process where the forged steel blade is heated up to approximately 760 °C (1,400 °F) dependent on the specific steel. This heating enables fast and uniform heating of the steel at the optimum temperature for maximum hardness. The tempering stage follows the hardening process, where the blade is heated in a bath of oil at a temperature between 200–400 °C (392–752 °F). Tempering imparts the steel its flexibility and toughness according to the phase diagrams for steel.  There are three types of steel blade according to the level of tempering it has received. Hard-tempered, medium-tempered and soft-tempered. Hard-tempered edges last longer but sharpening them is difficult. The converse is true for soft-tempered blades. The characteristics of medium-tempered blades are in-between the two extremes.