Impact properties of reduced activation ferritic/martensitic steel, F82H joined by hot isostatic pressing

Ogiwara, Hiroyuki; Tanigawa, Hiroyasu; Hirose, Takanori; Enoeda, Mikio; Koyama, Akira*

Reduced-activation ferritic/martensitic steels are leading candidate structural material for the blanket system of fusion reactors. The important issue in current stage is the finalization of detailed manufacturing specification for ITER test blanket module. Hot isostatic pressing (HIP) process is one of the most important methods to fabricate the first wall with cooling channels. The objective of this paper is to optimize HIP condition to obtain the excellent joints mechanical properties. The materials used were F82H steels. The joint was produced by solid state HIP method. Before HIP treatments, specimens were heated in vacuum condition to out-gas. This treatment was conducted to decrease oxidation on the surfaces. HIP treatments were carried out for 2 h at 1100 C - 140 MPa. The specimens were normalized at 960 C for 0.5 h and tempered at 750 C for 1.5 h. The bonding interface was characterized by scanning electron microscope. Charpy impact tests and tensile tests were conducted to evaluate the mechanical properties of HIP joint. Impact tests revealed that there were no significant difference in ductile-brittle transition temperatures of HIP jointed specimens and base metal specimens, but upper-shelf energy (USE) of HIP joint specimens at room temperature was about 10 % of that of base metal specimens. SEM observation on the fracture surface of HIP joint specimen revealed that a large number of oxides were formed on the HIP joint. This result indicates that oxides formed on the HIP joint are the dominant factor of the impact properties. Based on the results, the pre-HIP treatment conditions had been optimized to reduce the number of oxides, and USE of HIP joint specimen become about 50 % of base metal. The detailed analyses on HIP joint microstructure will be reported.