Residual stress in heat treatment of seamless steel tube

　　In sizing rolling, seamless steel pipe diameter is compressed at the same time, the wall thickness will also change, changes in diameter and ovality of the pipe depends mainly on the amount of reduction sizing, and if appropriate adjustment of the sizing press lower volume and temperature, it can eliminate the ovality of seamless steel tubes, while maintaining a predetermined diameter, which also allows seamless improved mechanical properties. However, during the seamless steel pipe sizing, but also make the pipe residual stress, reduce its mechanical strength.

　　The residual stress is a common method of project. Mechanism of heat treatment to reduce the welding residual stress is a view that the yield stress of the material increases as the heating temperature decreases, the elastic modulus of the material has declined, so the temperature of the heat treatment process requirements, internal welding materials residual stress exceeds the yield strength of the material at this temperature, plastic deformation occurs, the residual stress is because of this plastic deformation eased, but this time to eliminate the residual stress is limited, residual stress can not be reduced to The heat treatment temperature below the yield strength of the material. In accordance with this theory to develop a process generally choose a higher temperature. Another view is that the heat treatment to reduce the welding residual stress is caused by stress relaxation caused by the creep. Insulation material at higher temperatures, in the role of the internal residual stress will creep, causing stress relaxation and residual stress will drop. Theoretically if given enough time, you can completely eliminate the residual stress, residual stress and unlimited size.

　　In the sizing process, one seamless geometry is changed; the second is the contact surface contact with each other sizing rolls and seamless transfer of heat between the contact surfaces, and after contacting relationship change, separated from each other but also with Environmental medium heat exchange; Third seamless plastic deformation work volume will be converted into heat, and almost all the friction power irreversibly transformed into surface heat. However, since the time is short sizing rolling process, so heat roll and the environment is not sufficient, the temperature change is smaller rolling tube, in order to simplify the calculation, the temperature difference between the steel pipe can be neglected. Also, consider the amount of sizing seamless small elastic deformation of the roll sizing smaller,both strength and stiffness are significant differences between the sizing roll treated as a rigid body.