Mechanical properties of JK2LB at 4K

Abstract

The jacket of the central solenoid (CS) for ITER is designed to support cyclic tension load generated by the electro-magnetic hoop force during operation. Therefore, the CS jacket material requires high tensile strength, high ductility, and high resistance to fatigue. JK2LB was developed in Japan as a candidate material for CS jacket by using low carbon and boron additions in JK2. The preliminary data of mechanical property for JK2LB without cold work has shown improvement of ductility in comparison to JK2. As a routine multi-party verification process, a series of new mechanical tests including tensile, fatigue crack growth and fracture toughness have been carried out at 4K in MIT for both the base metal and welds of JK2LB. The test materials provided by JAREI were subjected to various cold work and aging before testing. It is found that the cold work has significant impact on the properties. Large variation of the tensile properties is observed. It includes a few specimens with brittle-like behavior. The fracture toughness of JK2LB is greatly reduced after cold work. High notch sensitivity at 4K is observed for side-grooved CT specimens. The current results indicate a need for more tests and studies.