2019 年 54 巻 6 号 p. 477-484
The hot isostatic pressing (HIP) diffusion bonding process is the one of rationalization processes to manufacture radial plates of superconducting magnets used in fusion reactor because of its small deformation and applicability to complex shapes. In order to establish the design and manufacturing processes, trials using small and actual-size prototypes have been carried out. The prototypes were manufactured using FM316LNH hot-rolled plates having a grain diameter of approximately 74 μm. The HIP bonding process makes the grains coarse and the tensile and fatigue strength are reduced. Meanwhile, forged FM316LNH has been applied to manufacture TF coils for the ITER. Based on the Hall-Petch relationship, since that material has a coarser grain diameter, approximately 125~177 μm, when this forged material is applied as base material for the HIP bonding process, a further reduction in mechanical properties can be observed. Accordingly, small prototypes with a diameter of 121 μm were used in the HIP bonding process in order to confirm HIP bonding quality, tensile properties at 4 K, 77 K and room temperature, and fatigue strength at 4 K. In addition, the relation between mechanical properties and grain size were summarized and a method for predicting tensile properties and fatigue strength based on the tensile properties and grain size was proposed.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.