Chinese researchers have developed a new ultra-strong cryogenic alloy, CHSN01, able to withstand stresses of up to 1.5 GPa at liquid helium temperatures while maintaining ductility at 30%, according to a report in Russia’s SecurityLab.
The development was based on Nitronic-50 steel, from which carbon was removed to below 0.01% to eliminate carbide formation. Next, we increased the nitrogen content to 0.30% and increased the proportion of nickel, ensuring the stability of the austenite phase at temperatures up to -269°C. The addition of vanadium in a highly tuned ratio has led to the formation of nanometre vanadium nitride particles that block dislocations and increase strength without compromising viscosity. Strict control of impurities – oxygen, phosphorus and sulphur (all below 0.02%) – eliminates defects that can initiate destruction under the influence of magnetic loads.
By leveraging existing production chains for Nitronic steel, mills in China were able to quickly transition to industrial production. By mid-2025, 500 tonnes of the new steel had already been delivered to the construction site of the BEST tokamak in Hefei. According to the lead physicist of the project, Li Lifeng, this confirms the alloy’s readiness for widespread adoption outside of laboratories.
The development, achieved after 12 years of intensive work, overcame the limitations of the traditional 316LN and JK2LB steels used in projects such as the International Thermonuclear Experimental Reactor (ITER) under construction in France. The main advantage of CHSN01 is its resistance to high loads and cyclic loading, which makes it a key element in the design of new generation superconducting tokamaks.
The new steel is superior not only in yield strength, but also in durability. Ripples, caused by the discrete nature of toroidal field coils, can lead to losses of energetic alpha particles (produced during fusion reactions) and affect plasma rotation, potentially hindering the achievement of sustained fusion. At 60,000 ripple conditions – this is how much a BEST tokamak requires over its lifetime – CHSN01 maintains degradation-free performance. In tests, the material was confirmed to withstand initial defects of up to 6 mm. This means lower requirements for cleanliness of processing, reduced component weight and cheaper assembly. Increased strength opens the way to more powerful magnetic fields.
CHSN01’s application capabilities go far beyond controlled thermonuclear fusion. Magnetic resonance imaging, particle accelerators, magnetic suspensions and even cryogenic components of quantum computers – all face a similar combination of cold and stress. The new material makes it possible to reduce the size of magnets and increase the service life of equipment.
