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Nine factors that affect heat treatment deformation (二)
- Dec 24, 2018 -

Fifth. Cold treatment and deformation


Cold treatment promotes martensite transformation, the temperature is lower, and the deformation is smaller than quenching and cooling, but the stress generated at this time is large, and cracking is easily caused by the superposition of residual stress, phase transformation stress and thermal stress.


Sixth, tempering and deformation


During the tempering process, the internal stress is uniformized, reduced or even disappeared, and the deformation of the workpiece tends to decrease, but at the same time, once the deformation occurs, it is difficult to correct. In order to correct such deformation, a method such as press tempering or shot peening is often employed.


Seven, repeated quenching and deformation


Normally, the workpiece after one quenching is repeatedly quenched without intermediate annealing, and the deformation is increased. Repeated quenching deformation, after repeated quenching, its deformation increases and tends to be spherical, prone to cracks, but the shape is relatively stable, no longer easy to deform, so intermediate annealing should be added before repeated quenching, the number of repeated quenching should be less than Equal to 2 times (excluding the first quenching).


Eighth. Residual stress and deformation


During the heating process, the steel is transformed from an elastomer to a plastomer at about 450 ° C, so it is easy to exhibit plastic deformation. At the same time, the residual stress will also disappear due to recrystallization when it is above this temperature. Therefore, during rapid heating, due to the temperature difference between the inside and the outside of the workpiece, the external temperature reaches 450 °C and becomes a plastic zone. When the internal temperature is low, there is residual stress and deformation occurs. After cooling, the region is where deformation occurs. Since it is difficult to achieve uniform and slow heating in the actual production process, it is very important to perform stress relief annealing before quenching. In addition to eliminating stress by heating, it is also effective to use vibration to eliminate stress on large parts.


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