Microstructure evolution of three‑roll skew‑rolling formed hollow axles with uniform wall thickness

The uniform thickness hollow axle is one of the lightest weight axles in the high-speed rail industry. It can effectively reduce unsprung mass and further improve the train speed. Therefore, due to its importance and significance, it is crucial to research and develop the uniform thickness hollow axle. To understand the microstructural evolution during three-roll skew-rolling (TRSR) forming, 30CrMoA alloy steel was used in this study. A constitutive model of 30CrMoA was established by SIMUFACT FORMING finite element software and utilized to simulate the deformation, heat transfer, and microstructure coupling during TRSR. Via analyzing the influence of process parameters on the average grain size, the microstructural evolution of the forming part at each deformation stage is revealed. The result shows that the dynamic recrystallization of the rolled piece produces a fine and uniform grain structure during the forming process. The refinement level is enhanced with the increase of the radial compression; the grain size is gradually increased from the outer surface to the inner surface of the rolled piece. At a higher rolling temperature, it was found the initial grain size and final average grain size were larger compared to the lower temperature. By increasing the axial traction speed, not only can the rolling time be shortened, but also the appearance of coarse grains can be avoided. Therefore, the mechanical properties can be improved.