Nobuyuki Fujitsuna

Development of low carbon and boron added 22Mn-13Cr-9Ni-1Mo-0.24N steel (JK2LB) for jacket which undergoes Nb/sub 3/Sn heat treatment

Japan Atomic Energy Research Institute has developed a low carbon and boron added 0.03C-22Mn-13Cr-9Ni-1Mo-0.24N-0.003B steel (JK2LB) for a conductor jacket of the central solenoid for the International Thermonuclear Experimental Reactor in collaboration with Kobe Steel Ltd. The feature of JK2LB is to have enough ductility and toughness after reaction heat treatment to produce Nb/sub 3/Sn. Tensile properties, fracture toughness, and fatigue crack propagation rate were measured at 4 K by using samples taken from an intermediate billet and the final jacket of JK2LB, which were produced with a mass production line. The average elongation and fracture toughness at 4 K after the heat treatment are 33% and 93 MPa/spl radic/m for the final jacket, and 30% and 121MPa/spl radic/m for the intermediate billet, respectively. The mechanical properties of weld metals were also evaluated and all data satisfied the ITER targets. It was also clarified that improvement of ductility and toughness were caused by reduction of chromium carbide precipitations due to low carbon and boron addition.

Demonstration of JK2LB Jacket Fabrication for ITER Central Solenoid

The Japan Atomic Energy Research Institute developed a jacket material called JK2LB (0.03C-22Mn-13Cr-9Ni-1Mo-0.2N-B) for the Central Solenoid (CS) conductor in the International Thermonuclear Experimental Reactor (ITER). To demonstrate production feasibility of CS conductor jacket, trial fabrication of a full size jacket using hot extrusion followed by cold drawing of the JK2LB billets was performed. As a result of dimensional measurement, the ITER dimensional requirement for circle-in-square jacket has been achievable. We achieved the requirement of 0.2% yield strength >1000 MPa and KIC(J)ges130 MParadicm for solution treated + aged jacket. It has been observed that applied cold work strongly affects the toughness of jacket before and after aging. We estimate that C and N reduction will be required to achieve the required strength and fracture toughness for ITER CS jacket. The fabrication R&D has prepared us for mass production of jacket for the ITER CS conductor procurement

Long-Term Isothermal Aging Behavior of V-Modified 2.25Cr-1Mo Steels

Long-term isothermal aging behavior up to 30,000h has been investigated in V-modified 2.25Cr-1Mo steels. When impurity elements were added, FATT in Charpy impact test vs. aging time curves showed basically of parabolic type, indicating the importance of segregation of impurities as the critical factor in controlling temper embrittlement. On the other hand, when the amount of impurities was small, FATT showed complex behavior with aging time. This suggests the importance of other factors in controlling temper embrittlement such as recovery of dislocations and enlargement of various carbide precipitates. When the degree of temper embrittlement after aging is compared in terms of the increase in FATT due to aging between the modified steels and the conventional 2.25Cr-1Mo steels, it is found to be small in the modified steel at the same impurity level (J-factor). It was also found that the modified steels showed no hydrogen embrittlement. No change was observed in FATT after hydrogen charge on the contrast to the conventional steel, which showed significant increase in FATT. This effect has been attributed to the small amount of diffusible hydrogen content in the modified steel by the presence of hydrogen trapping sites, which is present even after long-term isothermal aging.Copyright