Quenching and tempering of 45 steel

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Quenching and tempering of 45 steel

Postby hhm1020 » Sat Nov 10, 2018 1:46 am

45 steel is a medium carbon structural steel with good cold and hot working properties, good mechanical properties, low price and wide sources, so it is widely used. Its biggest weakness is that its hardenability is low, and the workpiece with large section size and high requirement is not suitable for use. The quenching temperature of 45 steel is A3+ (30~50) C, and in practice, the upper limit is generally taken. The high quenching temperature can accelerate the heating speed of the workpiece, reduce the surface oxidation, and improve the work efficiency. In order to homogenization the austenite of the workpiece, enough insulation time is needed. If the actual furnace load is large, it is necessary to extend the holding time appropriately.China Factory High Pressure Centrifugal Slurry Pump Zj Series
Otherwise, there may be a lack of hardness due to uneven heating. However, if the holding time is too long, there will also be serious defects such as coarse grains and oxidative decarbonization, which will affect the quenching quality. We believe that if the furnace load is greater than the technical documents, the heating and holding time should be extended by 1/5. Because the hardenability of the 45 steel is low, the 10% brine solution with high cooling rate should be used. The workpiece should be hardened after entering water, but not cooled. If the workpiece is cooled in brine, it may cause cracking of the workpiece. This is because when the workpiece is cooled to about 180 C, the rapid transformation of austenite into martensite causes excessive structural stress.2 kg Portable melting furnace for jewelry
Therefore, when the quenching workpiece is rapidly cooled to the temperature region, the slow cooling method should be adopted. Because the temperature of effluent is difficult to control, it must be operated by experience. When the shaking of the workpiece in the water stops, the effluent air-cooled (if oil-cooled is better). In addition, the workpiece enters the water should not be static, should be in accordance with the geometry of the workpiece, regular movement. Static cooling medium plus stationary workpiece results in uneven hardness and uneven stress, resulting in large deformation and even cracking of workpiece. The hardness of quenched and tempered 45 steel parts should reach HRC56-59, the possibility of large cross section is lower, but not lower than HRC48. Otherwise, it means that the workpiece has not been completely quenched, and there may be sorbite or even ferrite in the structure. This kind of structure is still retained in the matrix through tempering, which can not achieve the purpose of quenching and tempering. The quenching temperature of the 45 steel after tempering is usually 560~600 C, and the hardness requirement is HRC22~34. Because the purpose of quenching and tempering is to get comprehensive mechanical properties, the hardness range is wide. However, if the drawing has hardness requirements, the tempering temperature must be adjusted according to the requirements of the drawings, so as to ensure the hardness. For example, some axle parts require high strength and high hardness, while some gears and axle parts with keyway require lower hardness because of milling and inserting after quenching and tempering. As for tempering holding time, it depends on hardness requirement and workpiece size. We believe that the hardness after tempering depends on tempering temperature and has little relation with tempering time, but it must be reversed. Generally, the tempering holding time of workpiece is more than one hour.melting induction furnace for platinum from china supplier
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