Compositional requirements for the synthesis of Fe–Mn–C austenite-martensite composites: Beyond local equilibrium considerations in pearlite formation

Recently, a new generation of high strength steels was introduced by utilizing a lateral chemical pattern of an austenite stabilizer to create microstructures of austenite γ and martensite α’ after quenching. A ternary Fe-Mn-C pearlite is a suitable initial state for this if Mn effectively partitions into the cementite. In the present study, two model Fe-Mn-C alloys were pearlite treated outside the well-established local equilibrium, Mn partitioning regime (P-LE). A complete pearlite formation was achieved not only for Fe-3.0Mn-3.0C (at.%, Alloy A) at high pearlite formation temperature but also for Fe-6.9Mn-3.2C (at.%, Alloy B) at low transformation temperature. The morphology of the pearlite included fine-scaled fibers and lamellae. Even though outside the P-LE region, significant Mn partitioning into cementite was obtained for both alloys. Pearlite was formed at approximately the overall Mn content, while growing either enriched or depleted in C for most of the reaction. The successful application of a short time austenitization treatment was proven for both alloys transforming the pearlite into α’ + γ microstructures while retaining the initial pearlite morphology. Thus, fine-structured α’ + γ can be synthesized from pearlite processed well outside the established Mn partitioning regimes, opening a much larger compositional and processing space.