32Mn-7Cr austenitic steel for cryogenic applications

Large superconducting magnets used for magnetic fusion energy systems require structural alloys with high yield strength and sufficient toughness at very low temperatures. Most of the present large superconducting magnets use nitrogen-strengthened austenitic stainless steels. High-Mn steels are well known as another type of austenitic steel. Most of the conventional high-Mn steels, however, exhibit ductile-to-brittle transition behavior because of extremely high interstitial carbon and nitrogen contents. On the basis of extensive studies on the effects of alloying elements on low temperature mechanical properties, the authors have developed a 32Mn-7Cr austenitic steel with high yield strength, improved toughness, and very stable austenite at liquid helium temperature. The fabrication-related properties, such as machinability and weldability, were also improved to the same level as those of type 304 austenitic stainless steels