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In response to the ever increasing requirements for all materials that are used in superconducting magnets, this article deals with the possibilities of increasing the mechanical properties of a superalloy used at cryogenic conditions for structural reinforcement or conduit for supercnducting cables.
Typical structural materials for cryogenic temperatures down to 4.2 K are nickel-bearing austenitic stainless steels, especially the high-nitrogen 316LN austenitic steel. New research and development efforts were oriented towards new grades of superalloys which have not been tested and applied in cryogenic aplications so far. In these applications, excellent combinations of mechanical and physical properties are essential, such as resistance to neutron irradiation and corrosion. The aim of the experimental work was to compare the microstructures and mechanical properties at cryogenic temperatures in an age-hardenable nickel-molybdenum-chromium superalloy after various heat treatment sequences. Several types of precipitates were identified on grain boundaries. Microstructures and mechanical properties of the material were examined and tested. Deformation behaviour was investigated at temperatures ranging from room temperature down to 4.2 K. Scanning electron microscopy and electron backscatter diffraction were used to study the microstructure. The material exhibits high ductility and toughness even at low temperatures.