How China’s CHSN01 super steel could shrink fusion reactors, cut costs

China has developed a new high-strength steel alloy, CHSN01, designed to revolutionize fusion reactor construction by enabling smaller, more cost-effective tokamaks. Traditional fusion projects like ITER have relied on cryogenic stainless steels such as 316LN, which have yield strengths limited to about 0.9–1.1 GPa at liquid-helium temperatures and lose ductility after repeated stress cycles. These limitations cap ITER’s magnetic field at 11.8 tesla and necessitate large, expensive reactor designs. In contrast, CHSN01 can withstand magnetic fields up to 20 tesla and combined electromagnetic stresses of 1.3 GPa, while maintaining about 30% ductility before breaking. It also retains these properties after 60,000 on/off cycles, matching the operational demands of China’s Burning-Plasma Experimental Superconducting Tokamak (BEST). The alloy’s superior performance stems from precise chemical engineering: starting with a nitrogen-strengthened austenitic steel base (