Deformation Behavior of X70 Pipeline Steel Under Hot Straightening Condition

During the hot straightening process, the sheet undergoes multiple tensile and compressive deformation cycles. In this paper, cyclic tensile tests and microstructure observation under different strain amplitude, temperature, and strain rates were carried out. The macroscopic deformation behavior and microstructure evolution of X70 pipeline steel under cyclic tension and compression load were investigated, then, macroscopic mechanical properties and microstructure evolution of sheet steel in the process of hot straightening were deeply understood. The experimental results show that the X70 pipeline steel has the characteristics of cyclic hardening. Compared with temperature and strain rate, the hysteresis loop was dominantly influenced by strain amplitude. There is little difference between the peak value and the trough value of the circulating stress in the hysteresis loop. Hot straightening has little effect on the microstructure of the material. The study shows that the amount of deformation has a great influence on the deformation behavior of materials during the process of hot straightening, and the Bauschinger effect of materials is not obvious. The material deformation in the process of hot straightening belongs to the macroscopic deformation behavior.