Flow stress behavior, constitutive modeling, processing map and microstructure evolution in hot deformation of Fe-7.1Al-0.7Mn-0.4C-0.3Nb alloy

The automotive industry has experienced rapid growth, with lightweight materials becoming a significant research focus. Among these materials, low-density Fe-Mn-Al-C alloys show promise for this kind of application. To optimize the hot workability parameters of these alloys for practical applications, it is essential to explore the hot deformation behavior of these alloys. In this study, we investigated the hot deformation behavior of the low-density alloy Fe-0.77Mn-7.10Al-0.45C-0.31Nb using hot plane-strain compression tests for several deformation temperatures (850, 950, 1050, and 1150 °C) and nominal strain rates (0.01, 1, and 10 s-1). We observed unusual flow stress curves for low (0.01 s-1) and intermediate (1 s-1) strain rates, with discontinuous yielding and multiple stress peaks. This high-temperature behavior is associated with non-homogeneous strain partitioning in duplex microstructure (δ-ferrite + γ). Using the Zenner-Hollomon constitutive modeling approach, we estimated the thermal activation energy for hot deformation as 297 kJ/mol from the experimental peak flow stresses. Additionally, processing maps and microstructure correlation analysis revealed that the alloy exhibits good hot workability in the 975-1075 ºC temperature range under low and intermediate strain rates (0.01-0.3 s-1). Under these processing conditions, the δ-ferrite microstructure is submitted to dynamic recovery, while the austenitic phase undergoes dynamic recrystallization.