A comparative assessment of metallurgical and mechanical properties of two austenitic stainless steels for the conductor jacket of the ITER Central Solenoid

When energized, the ITER Central Solenoid (CS) coils will experience large cyclic electromagnetic forces that the conductor jacket itself must withstand. The jacket consists of circle-in-square extruded and drawn austenitic stainless steel pipes. High Mn-bearing austenitic stainless steels, such as the grade JK2LB selected for the jacket, feature a lower coefficient of thermal expansion between room temperature (RT) and 4 K than conventional AISI 300-series steels such as 316LN. The resulting smaller integral contraction will provide an additional precompression of the CS modules during cooling down. A comparative assessment of the results issued from jackets manufactured in both a modified 316LN with extra-low carbon (0.015% max.) and JK2LB by two different producers is presented and discussed, with a particular attention to the fracture mechanics behavior of the two steels and its correlation with tensile properties at cryogenic temperature.