Effect of temperature and time on the precipitation of κ-carbides in Fe-28Mn-10Al-0.8C low-density steels: Aging mechanism and its impact on material properties

In low-density steel, kappa-carbides primarily precipitate in the form of nanoscale particles within austenite grains. However, their precipitation within ferrite matrix grains has not been comprehensively explored, and the second-phase evolution mechanism during aging remains unclear. In this study, the crystallographic characteristics and morphological evolution of kappa-carbides in Fe-28Mn-10Al-0.8C (wt%) low-density steel at different aging temperatures and times and the impacts of these changes on the steels' microhardness and properties were comprehensively analyzed. Under different heat treatment conditions, intragranular kappa-carbides exhibited various morphological and crystallographic characteristics, such as acicular, spherical, and short rod-like shapes. At the initial stage of aging, acicular kappa-carbides primarily precipitated, accompanied by a few spherical carbides. kappa-Carbides grew and coarsened with aging time, the spherical carbides were considerably reduced, and rod-like carbides coarsened. Vickers hardness testing demonstrated that the material's hardness was affected by the volume fraction, morphology, and size of kappa-carbides. Extended aging at higher temperatures led to an increase in carbide size and volume fraction, resulting in a gradual rise in hardness. During deformation, the primary mechanisms for strengthening were dislocation strengthening and second-phase strengthening. Based on these findings, potential strategies for improving material strength are proposed.