Study on development policy for new cryogenic structural material for superconducting magnet of fusion reactor

•Mechanical properties at 4 K of XM-19 with 100 mm thick were measured.•Midsection of huge wrought showed lower strength. Nb segregation must be avoid.•Crystal refinement, precipitation by V and Nb and N solution strengthening are useful.•Area of over 1200 MPa yield stress and over 150 MPa√m fracture toughness is a new target.•Development policy of a new cryogenic structural material was presented. A fusion DEMO will require large-scale cryogenic structure including TF coil cases. Because of huge electromagnetic forces, extra thick plates and/or wrought products will be supplied. Since the midsection of the huge block is weaker than the block surface region, the design yield stress must be determined taking account of this lower strength part. To search the manufacturing process to improve the midsection strength, the crystal refinement strengthening and the precipitation strengthening are considered together with the carbon and nitrogen solid solution strengthening. XM-19 was focused based on the variation of the yield stress and the fracture toughness, a 100 mm thick block and a 30 mm thick plate were trial produced, and strength and the fracture toughness at the midsection were evaluated. This study will present the experimental data and discuss the development policy for a new cryogenic structural material for a fusion reactor.