Mechanical Properties of High Yield Strength High Manganese Steels at Cryogenic Temperatures

Abstract

Structural materials for large superconducting magnets of the next tokamak fusion reactors should have high yield strength with sufficient toughness at cryogenic temperatures. According to Japan Atomic Energy Research Institute¹ for example, the yield strength and the fracture toughness required are specified to be more than 1200 MPa and 200 ${\text{MPa}}\sqrt {\text{m}}$ at 4 K, respectively. The present work has investigated the effects of several metallurgical factors on mechanical properties of 32% Mn steels at cryogenic temperatures in order to obtain basic suggestions for developments of new high strength steels with high toughness for cryogenic uses. The 32% Mn steels have been examined in as-solution treated and aged conditions. The latter condition simulates the heat treatment for the precipitation of intermetallic compound Nb₃Sn. Structures used to support winding in the Wind and React method^2,3, or conductor sheaths will be heated together with the reacting materials, and it is demanded that the decrease in their strength and toughness during the heat treatment should be as small as possible.