Strength-ductility synergy in a 1.4 GPa austenitic steel with a heterogeneous lamellar microstructure

Abstract

Increasing the yield strength of austenitic steel without significantly sacrificing ductility has been a long-standing technical challenge. Here, we obtained an ultrahigh yield strength (∼1.4 GPa) and ductile (∼37% uniform elongation) austenitic steel through innovatively combining cold rolling, flash annealing, and tempering (CFT) processes. Such CFT steel shows a heterogeneous lamellar microstructure composed of reversed austenite and partially recrystallized austenite. The ultrahigh yield strength is attributed to the synergistic strengthening mechanisms induced by high-density dislocations, nano/ultrafine grains, and nanoscale precipitates. The achieved high ductility is associated with the pronounced transformation-induced plasticity (TRIP) effect induced by the high-density dislocations combined with the twinning-induced plasticity (TWIP) effect induced by grain refinement. Such a strengthening and plasticity mechanism paves the way for a processing route to achieve ultrahigh strength-high ductility combination in austenitic steel.