Abstract
The structural materials of the large superconducting coils for the next engineering tokamak (NET), which is now being designed at the Japan Atomic Energy Research Institute (JAERI), have to withstand magnetic forces as large as 1400MPa which corresponds to a strain of 0.2% at liquid helium temperature. We have been developing new materials instead of 304 and 316 austenitic stainless steels because the yield strength of the austenitic stainless steels is too low for them to be used for the structure of the NET, as shown by our various mechanical test results from room temperature to liquid helium temperature. As one of the new materials, high Mn austenitic steel (32Mn-7Cr) was selected and tested in a 10-ton cryogenic tensile test machine at 4K. The test results show the material has enough strength (1100MPa) and sufficient toughness at 4K to be used as the structure of the large superconducting coils.
