Effect of grain interior and grain boundary κ-carbides on the strain hardening behavior of medium-Mn lightweight steels

The present work aims to reveal the influence of κ-carbides precipitated in grain interior (GI) and along grain boundaries (GBs) with various characteristics on the strain hardening behavior of Fe–11Mn-(7, 10)Al-(0.6, 0.9, 1.2)C steels. Because of the higher probability for moving dislocations meeting with κ-carbides and shearing them, the increase in the volume fraction of shearable nano κ-carbides is more favorable for the improvement of the yield strength (YS) but thus induces the lower strain hardening rate (SHR), especially at low strains. The SHR maintains almost constant values even gradually increases during straining as the enhanced κ-carbide precipitation is beneficial to the planar glide softening and thus promotes the slip bands refinement. EBSD and TEM analysis reveal that both the unshearable coarse and sub-micron κ-carbides formed along GBs and in GI hinder the dislocation movement, and the former results in the significant strain localization in α/κ interfaces, consequently bringing about high SHR but premature failure. It is hoped that these findings will help achieving better synergy of strength and ductility of lightweight steels by utilization of the unshearable sub-micron κ-carbide in addition to the shearable one and partial-recrystallization.