The internal stress of a steel ball refers to the stress that exists in the material itself and is not affected by external forces to maintain its own balance.
The stress in the steel sphere is usually due to the deformation caused by the action of external forces during processing, as well as the internal force generated by interaction in the metallographic structure inside the steel to resist this external force, and try to restore the object from the position after deformation to the position before deformation, and keep the roundness of the steel sphere not deformed.
However, if there is internal stress inside the steel ball, cracks are easy to occur on the surface of the steel ball during long-term grinding and use. Due to the combined action of the spherical force and external force, the spherical surface is easy to become brittle, and the spherical surface will crack during the grinding and polishing process. Therefore, the stress inside the steel ball must be eliminated.