How does the residual stress of thick-walled seamless steel pipes occur during cold drawing?

How does the thick-walled seamless steel pipe produce residual stress during cold drawing? The uneven deformation of the thick-walled seamless steel pipe under the additional stress cold drawing results in the residual stress after cold drawing.

The applications of high-precision thick-walled seamless steel pipes are very wide. The thick-walled seamless steel pipes for general purposes are cold-rolled from ordinary carbon steel, low-alloy tool steel or alloy tool steel, with the largest production volume, and are mainly used as pipelines or structural parts for transporting liquids.

The thick-walled seamless steel pipe has a hollow cross-section, and many of them are used as pipelines for transporting liquids, such as pipelines for transporting crude oil, natural gas, liquefied gas, water and some solid materials. Compared with solid steel plates such as garden steel, seamless steel pipes have a lighter weight when the bending strength and torsional strength are the same, and are an economic cross-section stainless steel plate. The production process of thick-walled seamless steel pipe manufacturers can be divided into cold drawing and hot rolling. The production process of hot-rolled thick-walled seamless steel pipe is generally more complicated than hot rolling. The pipe material must first be subjected to a three-roll rolling mill, and the die test must be carried out after extrusion. If the surface initialization fails and cracks, the round steel pipe must be cut by a cutting machine and cut into a blank of about one meter in length.

The non-uniform deformation level of the thick-walled seamless steel pipe determines the size and distribution of the residual stress. The cold drawing deformation of the thick-walled seamless steel pipe is determined by its deformation characteristics. Because there is no mandrel in the drawing process, the deformation is slightly different from the deformation of the wall thickness change, the deformation state and the inner and outer double-layer deformation of the thick-walled seamless steel pipe are very different, resulting in uneven deformation.

During the deformation process of thick-walled seamless steel pipe, the metal material on the inner surface of the thick-walled seamless steel pipe reaches the state of plastic deformation, and the metal material flow in the radial direction is subjected to friction, so the radial deformation is uneven along the wall thickness, resulting in the natural tensile strength of the thick-walled seamless steel pipe surface layer significantly lower than that of the inner layer. In this way, the generation of additional radial and radial tensile deformation and additional stress reaches the highest value on the surface of the thick-walled seamless steel pipe; conversely, the additional compression deformation and compression stress generated in the thick-walled seamless steel pipe also reach the highest value, and the additional stress becomes residual stress deformation and remains in the pipe.

In short, the uneven deformation of thick-walled seamless steel pipe after drawing causes the residual stress of thick-walled seamless steel pipe to be large. Therefore, it is necessary to find an effective way to reduce the residual stress during drawing and reduce the vertical gap damage.