A Systematic Review of Medium-Mn Steels with an Assessment of Fatigue Behavior

Deformation-induced mechanisms, namely, transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), are primarily responsible for improved tensile properties in medium-Mn steels. Additionally, lower density and processing costs make these steels useful in various industries, particularly the automotive industry, which mandates a good understanding of underlying processing-microstructure-property correlations. Therefore, the present study reviews different thermomechanical processes and corresponding microstructural evolutions, followed by mechanical properties. In addition, an assessment of the fatigue behavior of medium-Mn steels based on duplex or multiphase microstructure and associated mechanisms has been presented. In high-cycle fatigue (HCF) loading, strain-induced martensite formation through TRIP at the crack tip is a barrier to dislocation motion. It deviates the crack propagation path to adjacent phases, which results in higher fatigue life. On the other hand, relatively high martensite boundaries initiate microcracks and accelerate crack propagation, resulting in lower life in low-cycle fatigue (LCF). However, the TWIP mechanism prevents cyclic softening and promotes cyclic saturation, extending fatigue life. The compositions of medium-Mn steel for enhanced fatigue resistance have been proposed. To that end, it is hypothesized that the TRIP + TWIP mechanisms lead to exceptional LCF performance. Further, microalloyed medium-Mn steels are expected to exhibit improved LCF and HCF behavior. Different thermomechanical processes and their corresponding microstructural evolutions are extensively reviewed, followed by discussion of mechanical properties, including fatigue behavior in medium-Mn steels. After considering various parameters, two design criteria are established. The transformation-induced plasticity + twinning-induced plasticity (region A) mechanisms result in excellent low-cycle fatigue (LCF) performance. In contrast, microalloyed medium-Mn steels (regions B and C) tend to exhibit enhanced LCF and high-cycle fatigue resistance.image (c) 2023 WILEY-VCH GmbH