Element partitioning effect on microstructure and mechanical property of the micro-laminated Fe-Mn-Al-C dual phase steel

In this study, a series of hot rolled steels with micro-laminated dual phase microstructure were annealed at various temperatures with different time durations. Due to the addition of aluminum, both the first partition of C, Mn, Al elements in the dual phase region at high temperature and the second partition of these elements in the decomposition of martensite happened in these steels. These steels annealed at 650 °C and 750 °C are composed of unchanged ferrite lamellae and mixed martensite phase, the latter one includes new ferrite, martensite and austenite phases. It shows that element partition has great effect on the microstructure and mechanical property of these micro-laminated Fe-Mn-Al-C dual phase steels. The enhanced mechanical properties, both strength and elongation, of the steels annealed at 750 °C are attributed to the relatively low stable austenite and the mixed martensite/austenite (M/A)+ferrite microstructure. The austenite volume fraction in the steels annealed at 750 °C decreases with the annealing time, which is attributed to the decrease of the austenite stability. The local compositions were measured to discuss with the formation of austenite with different volume fractions and stabilities. The results show that the partition of elements, especially for C, has great effect on the austenite stability in these steels.