Yield Strength Enhancement Without Ductility Loss Through Controlling the Intercritical Annealing Time in Medium‐Mn Steels

Abstract

Herein, the effect of shortening the intercritical annealing (IA) time in a two‐step process “intercritical annealing and tempering (IAT)” on the microstructure and the mechanical properties of medium‐manganese steel (MMnS) made of Fe–0.05C–7Mn–1.5Cu–1.5Ni–1.5Al–1.5Si–0.5Mo (wt%) and containing copper‐rich (CRP) and Ni(Al/Mn) precipitates is investigated. The atom probe tomography (APT), electron backscattering diffraction (EBSD), and the synchrotron X‐ray diffraction (SYXRD) are used to study precipitation, phase microstructure evolution, the austenite stability, and deformation mechanisms. Shortening the IA step, which is carried out at 700 °C, from 2 min (IAT‐2) to 1 min (IAT‐1), results in a yield strength (YS) increment of around 218 MPa with less than 1% loss of ductility. While the enhanced yield strength in IAT‐1 is attributed to the four times higher precipitates’ number density (n), the insignificant loss of ductility is attributed to the enhanced austenite stability factor from 4.5 to 9.2 in IAT‐2 and IAT‐1, respectively. The simultaneous increase in YS without ductility loss reflects that controlling the IA time is a promising strategy to overcome the yield strength and ductility trade‐off without the need for higher additions of costly alloying elements such as Ni, Al, Mn, and Cu.