Non-uniform deformation of seamless tubes during cold drawing results in additional stresses. After cold drawing, this additional stress still exists in the residual stress of the tube. The degree of uneven deformation of seamless steel tube determines the magnitude and distribution of residual stress.


Deformation of cold drawn steel is determined by deformation characteristics. Because the tube wall processing does not involve the axis in the stretching process, the thickness of the tube wall changes little after deformation, so the deformation conditions and deformation conditions of the inner and outer layers lead to seamless tube, resulting in non-uniform deformation.




During the deformation process, the metal near the inner surface of the seamless tube first enters the plastic deformation state, and the metal flows along the axis without being affected by friction. As a result, the axial deformation along the thickness direction is not uniform, and the natural elongation of the outer layer of seamless tube is lower than that of the inner layer. In this way, the additional axial and tangential tensile deformation and additional tensile stress of the outer layer are the largest. On the contrary, when the maximum stress is reached, the axial and tangential compressive deformation and compressive stress of the inner layer of the seamless tube are increased, and the residual stress in the tube after deformation is also increased.




In summary, due to the uneven deformation of seamless steel tube after air gap, the residual stress in seamless steel tube is larger. Therefore, it is necessary to find an effective way to reduce the residual stress of air pipe, so as to reduce the harm of vertical splitting.