Refined heterogeneous phase unit enhances ductility in quenched ultra-high strength steels

High ductility after quenching has significant benefits for ultra-high strength steels, especially from the perspective of formability. Intercritical annealing was applied prior to rapid quenching (flash) to obtain heterogeneous phase (HP) units, consisting of nano-twinned martensite and retained austenite. The uniform elongation was significantly enhanced without compromising ultimate tensile strength because of nanoscale twinned martensite and retained austenite. The formation of nanoscale twinned martensite and retained austenite occurred because of micro-segregation of alloying elements (Mn and Al) by combining annealing and flash process. Thermodynamic calculations enabled us to design the alloy and heat treatment.