The overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate speed to change its overall mechanical properties. Annealing, normalizing, quenching and tempering are the four basic processes in the overall heat treatment. They are called “four firesâ€, and the quenching and tempering are closely related, often used together, and are indispensable.
Understand the differences and effects of annealing, normalizing, quenching, and tempering:
Annealing : It is a heat treatment process that heats the workpiece to a suitable temperature, uses different holding time according to the material and the workpiece size, and then slowly cools with the furnace. The essence is to heat the steel after austenitizing and then transforming the pearlite. The purpose is to achieve or close to the equilibrium of the internal structure of the metal, to obtain good process performance and performance, or to prepare for further quenching.
Purpose and effect of annealing: reduce the hardness of steel, improve plasticity, to facilitate cutting and cold deformation processing; refine grains, eliminate structural defects caused by forging, welding, etc., uniform steel composition, improve steel properties or Prepare for subsequent heat treatment; eliminate internal stress in the steel to prevent deformation or cracking.
Normalizing: It is to cool the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to annealing, but the obtained structure is finer, which is often used to improve the cutting performance of materials, and sometimes used for some low requirements. The part is used as the final heat treatment.
Quenching: heating the workpiece to a certain temperature at a critical point for a certain period of time, rapidly cooling in a quenching medium such as water, oil or other inorganic salts or organic aqueous solutions to obtain martensite and/or bainite structure. Heat treatment process. After quenching, the steel becomes hard but becomes brittle at the same time.
The purpose of quenching is to transform the supercooled austenite into martensite (or bainite) to obtain martensite (or bainite) structure, and then mix with tempering at different temperatures to obtain the desired mechanical properties. Quenched workpieces are not allowed to be used directly in the field. Usually, tempering must be performed 1-2 times or more in real time to adjust the microstructure and stress.
Tempering: In order to reduce the brittleness of the steel, the quenched steel is heat- treated for a long time at a suitable temperature above room temperature and below 710 ° C, and then cooled. This process is called tempering.
Purpose and function of tempering: Reasonably adjust the mechanical properties to make the workpiece meet the requirements of use; stabilize the structure so that the workpiece does not undergo structural transformation during use, thereby ensuring the size and shape of the workpiece; reducing or eliminating the internal stress of quenching, Reduces deformation of the workpiece and prevents cracking.
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