Impact toughness and fracture behaviour of a lamellar structural Fe–Mn–Al–C cryogenic steel

In this work, a nickel-free Fe–Mn–Al–C lightweight structural steel for cryogenic application was developed. Based on the quenching-tempering (Q-T) process, the samples were heated to 650, 700, 750 and 800 °C and then quenched and tempered at 200 °C. The microstructure evolution and impact toughness of the tested steel were studied by X-ray diffraction, OM, SEM, TEM and EPMA. The microstructure is mainly composed of δ-ferrite, tempered martensite and retained austenite. The partition of carbon and manganese elements affected the stability of austenite in the steels, resulting in the reduction of the TRIP effect. The lamellar structure was beneficial to the strength and the cryogenic impact toughness of the steel and improved the plastic deformation ability during deformation.