Abstract: At present, the most mature low-temperature superconductor (LTS) is the Nb₃Sn superconductor, and YBCO in high-temperature superconductor (HTS) has become a candidate material for superconducting coils in China Fusion Engineering Test Reactor (CFETR) because of its excellent properties and no need for heat treatment. However, the mechanical properties of 316L, 316LN, JK2LB and other jacket materials do not meet the requirements of future superconducting magnets at low temperatures. Therefore, taking N50H austenitic stainless steel as the research object, the mechanical properties of the cold-worked specimens after heat treatment were tested to explore the effect of heat treatment on the mechanical properties of the N50H stainless steel. The results show that before heat treatment, the tensile strength of the N50H stainless steel is about 1800 MPa and the yield strength is above 1500 MPa at 4.2 K. After the two Nb₃Sn heat treatments, the tensile strength of the N50H stainless steel increases to more than 1800 MPa, and the yield strength is slightly higher than that without heat treatment. At the same time, the elongation is higher than 25% after both heat treatments and the maximum change is 5% compared with that without heat treatment. These further verifie the feasibility of the N50H stainless steel as YBCO and Nb₃Sn CICC jacket material in the future.

Key words: heat treatment, N50H steel, CICC jacket, mechanical properties