There are two types of heat treatment deformation of forgings: one is volume deformation, which is caused by different volume when the structure is transformed; the other is shape distortion, which is caused by uneven plastic deformation under the combined action of various complex stresses. In fact, due to the complex shape of the forgings in production and the various influences of various factors of the process operation, these two forms of deformation rarely exist alone, but for a specific forging and heat treatment process, the deformation may be in one form. Mainly.
1. Volume deformation of workpiece heat treatment
Different tissues have different volumes. The volume deformation of the forgings due to the volume difference caused by the phase change during heat treatment heating and cooling can be estimated based on the volume of each phase and the relative amount of each phase. Carbon content refers to the mass fraction of actual carbon in the matrix structure. The volumetric deformation is characterized in that the dimensions of the various parts of the workpiece expand or contract at the same rate and do not change the shape of the workpiece.
2. Shape distortion of workpiece heat treatment
During the heat treatment and heating process, the yield strength of steel decreases with the increase of temperature. When the residual stress of some parts of the workpiece reaches its yield strength, it will cause uneven plastic deformation of the forging and cause shape distortion and residual stress. relaxation. As can be seen from the previous analysis, the thermal stress and the tissue stress generated when the workpiece is cooled have a greater influence on the deformation of the workpiece than when the forging is heated.
The main causes of distortion of the shape of the heat treatment of the workpiece are: too intense heating or uneven heating, resulting in large internal and external temperature differences; excessive cooling or uneven cooling, resulting in large temperature differences of various sections; support for heating or cooling Improper holding; processing stress remaining in various machining; stress imbalance caused by uneven internal structure of the workpiece; stress imbalance caused by shape characteristics of the workpiece; unevenness of tissue transformation, that is, uneven volume ratio of each part of the workpiece Stress caused by changes, etc.
Shape distortion is the most common form of heat treatment. It is characterized by a change in the shape of the workpiece, which is manifested by the warp and distortion of the geometry.