Study on the shear-torsion deformation of rotary tube piercing process for nickel base superalloy

Abstract The separation layer defects (SLD) caused by shear-torsion deformation hinder the application of rotary tube piercing (RTP) process in the preparation of thick-walled tubes of nickel-base superalloy (TWNS). In this study, the influences of process parameters on the shear-torsion deformation of RTP process were studied, and the mathematic models between shear-torsion deformation and process parameters were established. The corresponding experiments were conducted to verify the simulation results, and the influences of shear-torsion deformation on the SLD and microstructure evolution were discussed. The results reveal that the SLD are attributed to the local shear/tensile stress near rolls and plug caused by the increases of circumferential shear deformation and longitudinal shear deformation under the condition of excessive roll speed and reduction rate. The increase of longitudinal shear deformation and circumferential shear deformation at the same time provides conditions for the generation of cracks, and the circumferential shear deformation directly leads to the propagation of SLD since the crack propagation direction is consistent with that of circumferential shear deformation. Under the common influences of compression deformation and shear-torsion deformation, the average grain size was significantly refined to 7-15 μm after single pass RTP process. The IPF map reveals that the three-dimensional shear-torsion deformation of RTP process is beneficial to the coordinated deformation of grains in all directions, and the dynamic recrystallization (DRX) grains without preferred orientation were obtained.