Heat treatment
Annealing
Annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness. Annealing is to heat the material slowly to the appropriate temperature, soak it, and then allow it to cool slowly by either burying the material in an insulating material or by simply turning off the furnace and letting both the furnace and the material cool slowly.
Quenching
Quenching is a heat treatment used to harden steel or iron alloys by inducing a martensite transformation. Quenching is to heat the material to a certain temperature, depending on the material, and keep temperature throughout the workpiece uniform, then rapidly cool the workpiece in water, oil or air.
Tempering
Tempering is a heat treatment usually performed after quenching/hardening, to reduce brittleness, relieve the internal stresses and remove some of the excess hardness. Tempering is to heat the material to a set temperature below its quenching/hardening, hold the workpiece at that temperature for a specific period, then cool the workpiece, typically in still air.