Quenching and tempering treatment refers to a dual heat treatment method of quenching and high-temperature tempering, which aims to ensure that the workpiece has good comprehensive mechanical properties. High temperature tempering refers to tempering between 500-650 ℃. Most quenched and tempered parts work under relatively large dynamic loads, and they bear the effects of tension, compression, bending, torsion or shear. Some surfaces also have friction, requiring certain wear resistance, and so on. In short, the parts work under various composite stresses. These types of parts are mainly structural components of various machines and mechanisms, such as shafts, connecting rods, studs, gears, etc., and are widely used in manufacturing industries such as machine tools, automobiles, and tractors. Especially for large components in heavy machine manufacturing, quenching and tempering treatment is more commonly used. Therefore, quenching and tempering treatment plays a very important role in heat treatment. In mechanical products, the performance requirements for quenched and tempered components are not entirely the same due to their different stress conditions. Various quenched and tempered parts should have excellent comprehensive mechanical properties, namely a suitable combination of high strength and high toughness, to ensure the long-term smooth operation of the parts.
Quenching is the first step of the process, and the heating temperature depends on the composition of the steel, while the quenching medium is selected based on the hardenability of the steel and the size of the steel component. After quenching, the internal stress of steel is high and brittle, and tempering is necessary to eliminate stress, increase toughness, and adjust strength. Tempering is the most important process for normalizing the mechanical properties of quenched and tempered steel. The curve of the mechanical properties of various steels changing with the tempering temperature, also known as the tempering curve of steel, can be used as a basis for selecting the tempering temperature. For high-temperature tempering of certain alloy quenched and tempered steels, attention should be paid to preventing the occurrence of the second type of temper brittleness to ensure the usability of the steel. [2]
Quenching and tempering treatment is widely used for structural parts that require excellent comprehensive performance, especially those that operate under alternating loads, such as automotive shafts, gears, turbine shafts of aircraft engines, compressor discs, etc. Structural steel parts that require induction heating quenching are usually quenched and tempered before surface quenching to obtain a fine and uniform sorbate, which is beneficial for the surface hardening layer and can also achieve good comprehensive mechanical properties at the core. Nitride parts undergo quenching and tempering treatment before nitriding, which can improve the processing performance of steel and prepare the structure for nitriding. To achieve a high smoothness of the measuring tool before quenching, eliminate stress caused by rough machining, reduce quenching deformation, and make the hardness after quenching high and uniform, quenching and tempering treatment can be carried out before precision machining. For tool steels with network carbides or coarse grains after forging, quenching and tempering treatment can be used to eliminate the carbide network and refine the grains, while spheroid zing the carbides to improve machinability and prepare the microstructure for final heat treatment.
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Grace Ma
Post time: Oct-31-2023
