Common Heat Treatment Concepts

 Common Heat Treatment Concepts
1. Normalizing: heating steel or steel parts to an appropriate temperature above the critical point AC3 or ACM for a certain period of time and then cooling in the air to obtain a heat treatment process for pearlite-like structure.
2. Annealing: heat the hypoeutectoid steel workpiece to 20-40 degrees above AC3, after holding it for a period of time, it is slowly cooled with the furnace (or buried in sand or lime) to below 500 degrees and cooled in the air. Craft
3. Solution heat treatment: heat the alloy to a high-temperature single-phase zone and maintain it at a constant temperature, so that the excess phase is fully dissolved into the solid solution, and then quickly cooled to obtain the heat treatment process of the supersaturated solid solution
4. Aging: After solution heat treatment or cold plastic deformation, the performance of the alloy changes with time when it is placed at room temperature or kept slightly above room temperature.
5.Solid solution treatment: fully dissolve various phases in the alloy, strengthen the solid solution, improve toughness and corrosion resistance, eliminate stress and soften, so as to continue processing and forming
6. Aging treatment: heat and keep warm at the temperature at which the strengthening phase precipitates, so that the strengthening phase precipitates out, hardened and improved strength
7. Quenching: A heat treatment process in which the steel is austenitized and cooled at an appropriate cooling rate to make the workpiece undergo martensite and other unstable structural transformations in the cross section or within a certain range
8. Tempering: the quenched workpiece is heated to an appropriate temperature below the critical point AC1 for a certain period of time, and then cooled by a method that meets the requirements to obtain the required structure and performance of the heat treatment process
Types and applications of tempering According to the different performance requirements of the workpiece, according to the different tempering temperature, tempering can be divided into the following types:
(1) Low temperature tempering (150-250 degrees) The structure obtained by low temperature tempering is tempered martensite. Its purpose is to reduce the internal stress and brittleness of quenched steel under the premise of maintaining high hardness and high wear resistance, so as to avoid cracking or premature damage during use. It is mainly used for various high-carbon cutting tools, measuring tools, cold punching dies, rolling bearings and carburized parts, etc. The hardness after tempering is generally HRC58-64.
(2) Intermediate temperature tempering (350-500 degrees) The structure obtained from intermediate temperature tempering is tempered troostite. Its purpose is to obtain high yield strength, elastic limit and high toughness. Therefore, it is mainly used for the treatment of various springs and hot work molds, and the hardness after tempering is generally HRC35-50.
(3) High temperature tempering (500-650 degrees) The structure obtained by high temperature tempering is tempered sorbite. Traditionally, the heat treatment combining quenching and high temperature tempering is called quenching and tempering treatment, and its purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness. Therefore, it is widely used in important structural parts of automobiles, tractors, and machine tools, such as connecting rods, bolts, gears and shafts. The hardness after tempering is generally HB200-330.
9. Carbonitriding of steel: Carbonitriding is the process of simultaneously infiltrating carbon and nitrogen into the surface of steel. Conventionally, carbonitriding is also called cyanidation. At present, medium temperature gas carbonitriding and low temperature gas carbonitriding (ie, gas nitrocarburizing) are widely used. The main purpose of medium temperature gas carbonitriding is to improve the hardness, wear resistance and fatigue strength of steel. Low-temperature gas carbonitriding is mainly nitriding, and its main purpose is to improve the wear resistance and seizure resistance of steel.
10. Quenching and tempering: It is generally used to combine the heat treatment of quenching and high temperature tempering as quenching and tempering. Quenching and tempering treatment is widely used in various important structural parts, especially those connecting rods, bolts, gears and shafts that work under alternating loads. After quenching and tempering, the tempered sorbite structure is obtained, and its mechanical properties are better than the normalized sorbite structure of the same hardness. Its hardness depends on the high temperature tempering temperature and is related to the tempering stability of the steel and the size of the workpiece section, generally between HB200-350.
11. Brazing: a heat treatment process for bonding two workpieces together with brazing filler metal
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