The uneven deformation of seamless tube during cold drawing leads to additional stress. After cold drawing, this extra stress remains in the residual stress of the tube. The degree of non-uniform deformation of seamless steel tube determines the size and distribution of residual stresses.
The deformation of the cold drawn steel is determined by the deformation characteristics. Because the tube wall processing does not involve the axis in drawing process, the thickness of the tube wall changes little after the deformation, so the deformation condition and the deformation condition of the inner and outer layers cause the seamless tube, which leads to the uneven 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 axial direction without being affected by friction caused by friction. As a result, the axial deformation of the thickness direction is uneven, and the natural elongation of the outer layer of the seamless tube is obviously lower than that of the inner layer. In this way, the axial and tangential additional tensile deformation and additional tensile stress of the outer layer are maximum. 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 added and the residual stress remaining in the tube after the deformation.
In summary, due to the uneven deformation of the seamless steel tube after the air gap, the residual stress in the seamless steel pipe is larger. Therefore, it is necessary to find an effective method to reduce the residual stress of the air tube to the harm of reducing the vertical splitting.