Steel Heat Treatment Terms
Annealing: The annealing process is intended to optimize the steel's machinability and formability. Quenched and tempered steel may not machine or bend very easily and annealing is often necessary to manufacture components economically. Annealing is used after cold forming operations, since during cold forming, the deformed areas may become work hardened and often fracture.
Normalizing: The process of normalizing consists of heating the steel to 1550° to 1650°F., for most low and medium carbon steels. The parts are then allowed to cool in still room temperature air. Normalizing can be described as a homogenizing or grain-refining treatment.
Quenching: A fully hardened steel is defined as having a 100% martensitic structure since that is the hardest structure obtainable. To ensure austenizing, the appropriate temperature must be reached for a sufficient amount of time. This is followed by rapid cooling (quenching) in water, oil, or air, with or without agitation, depending on the type of steel.
Tempering: This process is generally applied to hardened or quenched steel to improve mechanical properties, for the most part, tensile strength, ductility and toughness. Most steels are tempered between 400° and 1100°F.
Stress Relieving: When metal is heated, expansion occurs which is proportional to the temperature rise. Similarly, upon cooling, contraction occurs. Stresses are then set up. To relieve stresses, plain carbon steel is typically heated to 900° to 1100°F., then slowly cooled back to room temperature. Also known as stress relief annealing.