5th International High Manganese Steel Conference - HMNS 2022

Recently, the new designing concepts for medium-Mn steel have been promoted such as micro-alloyed steels to improve mechanical properties. Several authors reported that micro-alloying was effective to enhance the strength and toughness of medium-Mn steels. In this study, we elucidated the unknown role of micro-alloying element addition to a medium-Mn steel and explored why a micro-alloyed steel exhibited higher strength without sacrificing ductility as compared to a plain medium-Mn steel. Steels of Fe-8Mn-0.2C-3Al-(0, 0.2)V (wt.%) compositions, cold-rolled and intercritically annealed, were used as model alloys. The annealed steels revealed dual-phase microstructures consisting of α ferrite and γR retained austenite with globular morphology. V-added steel revealed a smaller grain sizes and lower volume fractions of γR than V-free steel owing to formation of VC precipitates. The precipitates were mostly formed in the α phase rather than in the γR phase. The VC precipitates led to different chemical composition of consisting phases of the steels; the V-added sample exhibited a lower C content in γR and a higher C content in α than the V-free steel. This difference in chemical composition of V-added steel, which was originated from VC formation, leads to an enhanced strain hardening rate (SHR) at the later stage of yielding by more active twinning-induced plasticity (TWIP) and dynamic strain aging (DSA).