Argonne National Laboratory is constructing a large superconducting MHD magnet to be used in the Coal-Fired Flow Facility (CFFF) at the University of Tennessee Space Institute. Measurements of the mechanical properties of all the materials used in the superstructure (bore tube, cast flanges and deposited weld metal, cast girder segments, aluminum girders, tie plates and connecting pins) have been performed. These measurements consisted of tensile strength, yield strength, % elongation, and reduction of area at 295, 76 and 4 K. Charpy "V" notch impact tests at 23 K were used for material acceptance with additional impacts done at 76 and 295 K. To verify ductility at the 4 K operating temperature, elastic-plastic J-integral fracture toughness tests at 295, 76 and 4 K along with associated fatigue crack growth rate data were generated. Results of these measurements are discussed.