Achieving high strength and ductility in Fe–Mn–Al–C austenitic steel via vanadium microalloying and aging

Abstract

An investigation was performed to evaluate the effect of vanadium (V) addition on the microstructure and the tensile behavior of Fe–27Mn–8Al-1.0C austenite lightweight steel after annealing and subsequently aging. The grain size of austenite in V-added steels was effectively refined and many nano-sized VC particles were observed in the austenite grains, compared to V-free steels, under annealed conditions. Subsequent aging promotes the precipitation of κ-carbide from the austenite matrix, and the dual-nanoprecipitation consisting of nano-sized VC and κ-carbide particles further improves the strength of the steel. Because of this, the current steels have good ductility (up to 41% total elongation) even when aged and high yield and ultimate tensile strengths of up to 1009 MPa and 1243 MPa, respectively. By examining the dislocation structure of the specimens during deformation, it was also possible to determine how precipitates affected the rate of strain hardening. As a result, the strain hardening rate of the V-added steel after aging is effectively improved at the initial deformation by the precipitation of VC particles, which compensates for the decrease in strain hardening rate due to shearable κ-carbide. This study provides a strategy to obtain an excellent combination of strength and ductility in lightweight steel by V microalloying and simple thermomechanical treatment.