When quenching a large section workpiece of 40Cr steel, the key points that should be taken into account in order to avoid quenching cracks, affected zone and deformation include the proper selection of the quenching medium, the preparation of the quenching furnace, and controlling quenching process parameters such as heating and cooling rate, minimizing distortion and reducing residual stress. The quenching temperature of the workpiece is vital for obtaining good quality and high strength of the workpiece. The cooling rate of 40Cr steel large section workpiece is usually 10-12 °C / s, but the heating rate should be considered to prevent the formation of quenching cracks. With the development of industrial technology, high-frequency quenching can be used to obtain high cooling rate, uniform microstructure and stable performance of the parts.
The crystallization process of quenching involves the continuous transformation of austenite, martensite and other microstructures at different temperatures. The transformation temperature is influenced by different quenching mediums. Usually parts are quenched with quenching oil or water. The quenching oil has good thermostability and it can control the hardness and toughness of the components. And the cooling rate is steady and controllable. The use of water quenching is usually used to obtain a larger volume change to achieve an improved service life.
Quenching microstructure of workpieces A, B, C and D
Shows the quenched microstructures of 40Cr steel large section workpieces A, B, C and D, which quenched with oil, water and high-frequency electric current respectively. It can be seen that the microstructure of workpiece A quenched with quenching oil consists of fine martensite, some tempered martensite and a small amount of pearlite. Workpiece B was quenched with water, resulting in a microstructure of large martensite grains, a small amount of tempered martensite and polymorphous tissue. The microstructure of workpiece C quenched by high-frequency current consists mainly of tempered martensite and relatively uniform dispersed pearlite. The workpiece D quenched by high frequency current has more uniform distributed tempered martensite and retained austenite.
In summary, quenching is an important process for improving the strength, hardness and wear resistance of 40Cr steel large section workpieces. In order to obtain reliable quality of large section workpieces, proper selection of quenching method and processing parameters should be used to ensure that desired physical and mechanical properties can be obtained. The quenching microstructure is mainly composed of martensite, tempered martensite and pearlite. The microstructure of workpiece quenched by high frequency current has more uniform distributed tempered martensite and retained austenite.
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