(1) Reasonably adjust the hardness and strength of steel, improve the toughness of steel and make the workpiece meet the performance requirements. For example, the hardness and wear resistance of cutting tools, measuring tools, and molds can be improved by tempering, and the strength and toughness of various machine parts can be improved.
(2) Both quenched martensite and residual austenite are unstable structures, which will decompose during work, resulting in changes in the size of parts, which is not allowed for precision parts. Tempering can stabilize the structure so that the workpiece will not undergo structural changes during long-term use, thereby stabilizing the shape and size of the workpiece.
(3) Reduce or eliminate the workpiece's quenching internal stress to reduce the workpiece's deformation and prevent cracking.

Generally, quenching is performed to achieve the following purposes:
(1) Increase the hardness and wear resistance of the workpiece. For example, various tools, carburized parts, and parts that require surface wear resistance (gears, rollers, etc.) must be quenched and then tempered at low temperatures to improve their hardness and wear resistance.
(2) Quenching is performed to obtain certain mechanical properties for subsequent tempering, such as various springs and quenched and tempered workpieces. Their quenching is not to increase hardness, but to obtain a certain hardness, elasticity, toughness, and other comprehensive mechanical properties in the subsequent tempering.
(3) In order to change certain physical and chemical properties of steel, such as quenching of magnetic steel (to increase magnetic permeability) and stainless steel (to obtain a uniform single-phase solid solution).

Mold steel quenching is heating the mold steel to a certain temperature and keep it warm for a certain period of time, and then quickly cooling it. This process is called quenching. The main purpose of quenching is to make all or most of the structure of the mold steel change to austenite, obtain high toughness, and then quench at an appropriate temperature so that the product workpiece has the expected properties. Quenching is an extremely critical task in the heat treatment method to achieve the required comprehensive physical properties and wear resistance. Whether it is successful depends mainly on the heating rate, quenching temperature, holding time, and subsequent cooling method. For the heating rate, the temperature rise is too slow during heating, the product workpiece is easy to oxidize and carburize, the service life of the workpiece is low, and the cost is increased. However, if the temperature is raised too high, the surface and the center of the mold will cause a temperature difference. The greater the temperature difference, the greater the internal stress, and therefore, the greater the probability of deformation cracking.

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