ress in many adjacent grains of the material. If the workpiece is cut or material is removed, the presence of macroresidual stresses into a workpiece by heat treatment or plastic deformation may also cause a distortion of the part. The pseudo-macroresidual stress is the average of the residual stress in many grains of one phase in a multiphase material minus the macroresidual stress in a part is the total residual stress minus the macroresidual and the pseudo-macroresidual stress. The thermal stress is approximately proportional to the temperature difference and is tensile in the surface and compressive in the core. Large thermal stresses are favored by low thermal conductivity, high heat capacity, and high thermal expansion coefficient. Other factors increasing the temperature difference and thermal stresses are large thickness dimensions and high-cooling intensity of the cooling medium. A large yield stress at elevated temperatures will decrease the degree of plastic flow and thus the residual stress, while the yield stress at the ambient temperature puts an upper limit on the residual stress. Cracking and Distortion due to HardeningThere is a risk for cracking of a workpiece if large tensile stresses, transient or residual, are combined with the presence of a brittle microstructure. Thermal stresses during cooling generally increase with the size of a workpiece. For phase transformation-induced stresses, geometric dimension, hardenability of the steel, and quench intensity interact in complicated manner. However, as a general rule it holds that the use of a more efficient cooling medium, for example, water as compared to oil, will lead to larger stresses. The presence of geometric stress raisers increases the risk of cracking. Large tensile stresses in the core at lower temperatures may lead to center cracks even if the microstructure is not martensitic. Such a situation exists for larger diameter cylinders with a ma...
