斜轧穿孔法制备Ti80合金无缝管工艺分析

This paper deals with the simulation of rotary piercing process of Ti80 alloy seamless tube via a 3D thermal-mechanical coupling finite element model (FEM). The model can visualize the complex continuous piercing process from biting to steady piercing and to final drilling. Concurrently, the simulated results help to understand the mechanism of central fracturing as well as the distribution of physical fields. Combining normal stress state of (+, -, +) along the rolling centerline with non-negligible plastic deformation at the centre of the billet, the cavity formation was determined to be caused by plastic cracking under tensile stress. During the piercing process, the strain distribution was U1+W+2U2 along the axial direction and lamellar along the radial direction. The final equivalent strain of the hollow billet could reach 5~11. The strain rate in contact area between the blank surface and the discs was 0.71~3.6 s^-1, while that between the surface and the rolls was up to 4.6~26 s^-1. The relatively high strain rate was beneficial to the plastic deformation of raw material. The billet temperature in front of the plug was the highest, and the area in contact with the piercing tools decreased slightly. However, the vast majority of the billet in deformation zone was still in the single β phase field. Additionally, the loads on the plug and roll in the whole piercing process presented a typical three-stage distribution. The mean values in the stable phase were close to the experimental researches, which demonstrated the accuracy of the model. Based on the simulation of finite element method, the Ti80 alloy seamless tube has been successfully pierced through the experimental Diescher's mill. The microstructure of the tube was illustrated as a single Widmanstatten microstructure. Due to the severe deformation, the finer and equiaxed dynamic recrystallization β grains were formed from outer surface to the middle layer and to inner surface. The mechanical property test show that the strength and plasticity of the tube can meet the requirements of the project.