Delamination induced exceptional cryogenic toughness in ferrite/martensite dual-phase layered steels

The ductile-to-brittle transition (DBT) with decreasing temperature in Body-centered cubic (BCC) steels restricts their application in cryogenic environments. In this study, we design a ferrite/martensite dual-phase layered steel containing weak and continuous interfaces to overcome this limitation. Charpy impact tests demonstrate that the impact energy of L-F/M-750 steel rises steadily from 20 °C to −196 °C and reaching 400 J at −196 °C. Successive initiation and propagation of delamination cracks have been observed. These delamination events repeatedly reduce the stress triaxiality ahead of the crack tip, thereby enlarging plastic zones and substantially enhancing impact energy. The L-F/M-850 steel (red) exhibits a conventional ductile-to-brittle transition with decreasing temperature, whereas the L-F/M-750 steel (blue) displays a unique inverse temperature-dependent impact toughness.