Effect of circumferential wall thickness heterogeneity on the multi-pass expanding and drawing deformation characteristics of BFe10-1.6-1 cupronickel pipes

Based on Deform-3D software, this paper simulated the multi-pass expanding process of BFe10-1.6-1 cupronickel copper tubes under the conditions of uniform wall thickness tube billets and three kinds of uneven wall thickness, and obtained the tongue-shaped protrusion consistent with the actual production, investigated the impact of tube wall roundness and wall thickness inhomogeneity on stress, strain, damage, and wall thickness evolution during tube expanding process. Additionally, EBSD characterization was conducted on the tongue-shaped region. The findings indicate that internal wall uniformity and thin-walled regions substantially influence tube production and quality. Following four passes of expansion under the three distinct wall thickness inhomogeneity scenarios, it is observed that internal wall inhomogeneity leads to a 50~100 MPa increase in equivalent stress within the unexpanded part of the tube, accompanied by an overall damage value increment exceeding 0.05. Moreover, high levels of damage persist within the thin-walled region, making it more susceptible to defects. Despite multiple expansion passes, no improvement is achieved for the thin-walled region, which consistently maintains a suboptimal thickness ranging from 0.4 to 1.5 mm. Furthermore, compared with the typical regional structure after expanding, the uniform structure of the tongue region is poor, with significant grain size difference, low corrosion resistance, and poor comprehensive performance.