Mechanism Study and Optimized Technology of Multi-Pass Drawing Process for Ultrafine-Grained Inconel 718 Micro-Tubes

In this paper, Inconel 718 tube blanks are processed into ultrafine-grained Inconel 718 micro-tubes by multi-pass drawing. The mechanism of grain size variation and microstructure evolution has been discussed. Moreover, parameters of tubes have been compared and studied for each pass. Furthermore, optimized sequence on drawing process was determined. Optical microscope (OM) and surface roughness tester (SRT) were used for analyzing the evolution of tube size and surface roughness, separately. To further investigate the mechanical properties and microstructure of Inconel 718 tubes, tensile tests and microstructure analysis were conducted. Ultrafine-grained Inconel 718 micro-tubes with outer diameter of 0.9mm have been produced successfully. The results show that grains were continuously refined during the drawing process and low angle grain boundaries were finally obtained. On the other hand, plasticity reduced while the strength increased obviously with the drawing process. Compared with the results of two manufacturing plans (5 passes and 11 passes), the manufacturing plan with 7 drawing passes has been accepted as the most topgallant option due to its comprehensive advantages. In general, mechanism study and optimized technology of multi-pass drawing process for ultrafine-grained Inconel 718 micro-tubes were discussed in detail, which provide a theoretical basis for high precision micro-tubes manufacturing process with hardly deformable materials.