The reducing rate distribution is critical for the quality and precision of the final pipe during the process of stretch-reducing of the seamless pipe. The inhomogeneous deformation of the pipe may occur if the reducing rate distribution is improper. This paper analyzed the trend of the reducing rate distribution in terms of metal flow and put forward a “three-point and two-section converged” correction theory based on relevant research. In order to verify the theory, the finite element model is established according to the results obtained from the modified model. The simulation is accomplished successfully, and the cross-section of the pipe is evenly reduced with the longitudinal metal flowing uniformly. The result from the experiment is consistent with that from the simulation, which shows the rationality of this theory, providing a new method for the reduction rate allocation.

Tube continuous rolling (TCR) is a beneficial method for the production of titanium pipes due to its high efficiency and shorter process, with the mandrel playing a crucial role. The present study delved into the mechanism of the mandrel and its impact on the TCR process, through comprehensive analyses that included numerical simulations and experimental tests. The following conclusions were drawn: as the mandrel diameter coefficient increases, the area of the front slip zone gradually expands, and the tension changes from tensile stress to compressive stress. Additionally, the temperature exhibited an overall downward trend, while the strain distribution at the groove vertex and taper became more uneven. Concerning metallographic structure, instances where the mandrel diameter coefficient increases led to elongated, recrystallized grains at the groove vertex. The twinning quantity at the groove taper increased initially and then decreased, indicating a deformation mechanism shift from twinning to slip.

The continuous retained-mandrel rolling process is a promising method for titanium tube production with high efficiency and a short process. The importance of mandrel as a deformation tool supporting the inner wall is crucial. This paper thoroughly examines the influence of mandrel velocity on the deformation characteristics at the groove vertex using three approaches: numerical simulation, shear-deformation observation experiments, and microstructure analysis. The following conclusions are drawn: Decreasing the mandrel velocity enhances the penetration of shear deformation into the inner wall of the titanium tube, improves thickness uniformity, and shifts the deformation mechanism near the inner wall from twinning to dislocation slip. As a result, the volume fraction of recrystallization increases from 18.4% to 42.3%. However, the mean shear strain increases first and then decreases to a certain value as the mandrel speed decreases, which is attributed to the combined influence of the cross-shear zone and the rolling force.