Causes and control methods of residual stress after cold drawing of thick-walled seamless tubes

1. Generation of cold drawing stress

During the cold drawing process, thick-walled seamless tubes will produce uneven deformation due to additional stress, which will form residual stress after cold drawing. This high-precision thick-walled seamless steel pipe is widely used in many fields, such as pipelines or structural parts for transporting liquids. Its hollow cross-section design makes it relatively light in weight under the same bending, torsion and compressive strength, making it an economical cross-section steel.

In the process of cold drawing stress generation, the metal material on the surface of the thick-walled seamless tube first enters the plastic deformation state, and its radial metal fluidity is not hindered by friction, resulting in uneven radial deformation along the wall thickness direction. This phenomenon causes the natural tensile strength of the surface layer of the steel pipe to be significantly lower than that of the inner layer. Therefore, in the surface layer of the thick-walled seamless steel tube, the radial and axial tensile deformations and additional stresses reach the maximum value; in the opposite direction, the additional reduction deformation and reduction stress also reach the maximum value in the pipe. These additional stresses are converted into residual stresses after deformation and remain in the pipe. In summary, the uneven deformation of thick-walled seamless steel tubes after drawing is the main reason for the increase in residual stress.

2. Production process and its influence
The production process of thick-walled seamless tubes mainly includes cold drawing and hot rolling. The hot rolling process is relatively complicated and requires multiple processes, such as three-roll mill extrusion molding, die detection, surface initialization and cutting. During this process, if cracks or other defects appear on the surface of the steel pipe, it will be precisely cut by a cutting machine to ensure product quality.

3. Factors and influences of residual stress
The residual stress distribution and size of thick-walled seamless tubes are closely related to their uneven deformation level. This deformation characteristic is mainly attributed to specific conditions during cold drawing, such as lack of mandrel support and deformation differences caused by wall thickness changes. During the deformation process, the metal material on the inner surface of the thick-walled seamless steel pipe first enters the plastic deformation state, and its radial metal fluidity is not hindered by friction, resulting in uneven radial deformation along the wall thickness direction. This phenomenon causes the natural tensile strength of the surface of the steel pipe to be significantly lower than that of the inner layer.

Therefore, on the surface of the thick-walled seamless tube, the radial and axial tensile deformations and additional stresses reach their maximum values; in the opposite direction, the additional reduction deformation and reduction stress also reach their maximum values inside the pipe. These additional stresses are converted into residual stresses after deformation and remain in the pipe. 

In summary, the uneven deformation of the thick-walled seamless steel tube after drawing is the main reason for the increase in its residual stress. Therefore, it is necessary to explore methods that can effectively reduce the residual stress and reduce the vertical gap damage during the pipe drawing process.

Read more: Cold Drawn Seamless Tube for Mechanical & Hydraulic or Choosing seamless tubes: cold rolled vs. hot rolled