TRIAL FABRICATION OF HEAVY SECTION BASE METALS AND WELDED JOINTS FOR ITER TF COIL

摘要

Structural materials with high strength and toughness are required for the ITER toroidal field (TF) coils. The maximum thickness of base metal and weldments of the ITER TF coil case are about 250mm and 200mm, respectively, based on the current ITER design. In addition, thicker plates will be required in the construction of ITER to reduce the amount of welded structures in the coil case. Japan Atomic Energy Research Institute (JAERI) successfully developed the Japanese Cryogenic Steels which satisfy the ITER requirements (0.2% yield strength of over 1000 MPa and fracture toughness of over 200MPaVm) for plate thickness less than 140 mm. However, it has not been demonstrated then whether the JCS can retain their high strength and toughness in heavy-section forged products. Therefore, JAERI performed trial fabrication of JJ1 and JK2 forged plates of 250mm thickness and demonstrated TIG welding technique with narrow gap grooves for 200 mm thick plates. In addition, a trial fabrication of a 500 mm~t JJ1 forged block was performed to demonstrate production feasibility of thick forged plates which could be used in the coil cases. The mechanical properties of the 250mm~t base metal of JJ1 and JK2 satisfied the ITER requirement. In addition, the fully austenitic welded joints, which showed mechanical properties that were nearly the same as those of the base metals, were successfully produced without any cracks or harmful blowholes.