Exceptional fatigue-resistant austenitic stainless steel for cryogenic applications

Most alloys change from ductile to brittle at cryogenic temperatures, whereas high-entropy alloys show better strength, ductility, and toughness. However, they suffer from cost and mass-production challenges. We discerned the fatigue behaviour of a cost-effective austenitic stainless steel, SS316L, at an ultra-low temperature (ULT) of 15 K. For the cryogenic applications, our work demonstrates that compared to room-temperature (RT), ULT exhibits eight times higher fatigue life, despite even higher applied stress [ σmax=1.3×σysRT/ULT (280 MPaRT; 517 MPa15 K)]. At 15 K, the fatigue mechanisms involve stacking faults, a two-step martensitic phase transformation (γ→ϵ→α′) and α′-martensite twinning, utilizing the applied fatigue strain efficiently. The remarkable improvement in the mechanical strength and fatigue life at ULT is the key to revolutionizing sustainable advancements in space exploration and energy storage.