There are two types of heat treatment deformation: one is the change of size, the other is the change of part geometry. The main reason for the shape change of parts is the thermal stress and phase transformation stress during heat treatment, heating and quenching.

Heating speed is too fast, parts are too large relative to the heating furnace, and the temperature of each part is different, which will lead to thermal deformation. During heat preservation, the residual stress of processing will be released to produce deformation, and the self weight of parts will also cause deformation. During cooling, due to the different cooling rates at different parts of the part, thermal stress will be formed and the part will be deformed. Even if the cooling rate is the same, the cooling is always fast on the surface and slow on the heart.

Therefore, the surface with phase transformation first causes plastic deformation of the center without phase transformation. If there is segregation of alloy components or surface decarburization in the material, the phase transformation stress will be more uneven, which will easily lead to part deformation. In addition, if the thickness of parts is uneven, the cooling rate will be different.