There are two types of heat treatment deformation: one is the size change, the other two is the change of part geometry. Different methods of heat treatment, deformation and deformation prevention of parts size and geometry are also different.
The longer the holding time and the higher the temperature are, the more carbon is dissolved into austenite and the larger the expansion of martensite is. The expansion of martensite is the largest, followed by upper bainite, and the volume change of lower bainite and troostite is very small. At low temperature tempering, martensite shrinks and the amount of shrinkage is directly proportional to the supersaturated carbon content. When heated at room temperature of -200, part of austenite is transformed into martensite and expanded. However, the expansion of the martensite due to decomposition near 200 c has little change.
In conventional heat treatment, the main reason for the shape change of parts is the thermal stress and phase transformation stress during heat treatment and quenching. Excessive heating speed, relative to heating furnace parts are too large, parts of the temperature is different, will lead to thermal deformation. During heat preservation, the residual stress will be released and deformed, and the weight of the parts will also lead to deformation. When cooling, due to different parts of the cooling rate of different parts, will form thermal stress and deformation of parts. Even if the cooling speed is the same, the cooling surface is always fast and the heart is slow. Therefore, the surface of phase transformation causes plastic deformation of the core without phase transformation. If there is segregation of alloy composition or surface decarbonization in the material, the phase change stress is more inhomogeneous and the deformation of parts is more easily caused. In addition, if the thickness of the parts is uneven, the cooling rate will also be different.