Effect of Thickness Reduction on Residual Stress and Microstructure Inhomogeneity of Radial Forged Ni-Cr-Mo High-Strength Steel Tube

Radial forging is one of the most advanced technologies in barrel forming. The residual stress and microstructure inhomogeneity greatly affect the performance of the radial forged tube. In this work, the effect of thickness reduction on residual stress, microhardness, dislocation density, grain boundary content, and grain size of the radial forged tubes was studied. The influence of thickness reduction on the unevenness of strength was analyzed. The results showed that the residual stress gradually changed from compressive stress of the internal tube to tensile stress of the external tube. With the increase in forging reduction, the axial residual stress decreased, whereas the hoop stress changed slightly. The internal microhardness of the radial forged tube was greater than the external microhardness. The larger the forging reduction, the smaller is the difference in microhardness between the inner and outer surfaces of the tube. The grain boundary content, local misorientation, and dislocation density of the inner surface were greater than those of the outer surface. The unevenness of strength was influenced mainly by dislocation density. The microstructure was homogeneous when forging reduction was large. A large forging reduction is beneficial to improving the performance of the radial forged tube.