Formation of residual stress of seamless steel tube during cold drawing
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The non-uniform deformation of seamless steel tube becomes the residual stress after cold drawing under additional stress.Precision seamless steel tubes are widely used.General purpose seamless steel tubes are rolled from common carbon structural steels, low alloy structural steels or alloy structural steels to achieve the highest yield and are mainly used as conduits or structural parts for fluid delivery.Seamless steel pipe has a hollow section, a large number of fluid pipeline, such as the transportation of oil, natural gas, gas, water and some solid materials pipeline.Compared with round steel and other solid steel, steel pipe has the same bending and torsion strength and lighter weight. It is a kind of economic steel section.
Seamless steel tube manufacturer production process can be divided into cold drawing and hot rolled, cold rolled seamless steel tube production process generally more complicated than hot rolled, three-roll rolling tube billet must first, after the extrusion sizing test, if there is no response after crack on the surface of pipe have to be cut after cutting machine, cutting grow about a meter of billet.The degree of non-uniform deformation of seamless steel tube determines the magnitude and distribution of residual stress.The cold drawing deformation of seamless steel tube is determined by its deformation characteristics.Because there is no mandrer in the process of drawing, the deformation condition is very different from the deformation state of the inner and outer layers of seamless steel tube after little change of the thickness of the tube wall, resulting in uneven deformation.In the process of deformation, the metal on the inner surface of seamless steel tube first enters the plastic deformation state, and the metal flows along the axial direction without friction.
Therefore, the axial deformation along the wall thickness direction is not uniform, resulting in the natural elongation of the outer layer of seamless steel tube is significantly lower than the inner layer.Thus, additional axial and tangential tensile deformation and additional stress generation in the outer layer of seamless steel pipe reach the maximum value;On the contrary, the additional compression deformation and compression stress layer produced within the seamless steel tube also reach the maximum value, the additional stress becomes residual stress deformation, remaining in the tube.
In conclusion, the non-uniform deformation of seamless steel tube after drawing leads to the large residual stress of seamless steel tube.Therefore, it is necessary to seek for an effective method to reduce the longitudinal fracture damage during tube drawing and residual stress reduction.