Microstructure and Plasticity Evolution During Lüders Deformation in an Fe-5Mn-0.1C Medium-Mn Steel

Abstract

The local plasticity and associated microstructure evolution in Fe-5Mn-0.1C medium-Mn steel (wt.%) were investigated in this study. Specifically, the micro-deformation mechanism during Lüders banding was characterized based on multi-scale electron backscatter diffraction measurements and electron channeling contrast imaging. Similar to other medium-Mn steels, the Fe-5Mn-0.1C steel showed discontinuous macroscopic deformation, preferential plastic deformation in austenite, and deformation-induced martensitic transformation during Lüders deformation. Hexagonal close-packed martensite was also observed as an intermediate phase. Furthermore, an in-situ neutron diffraction experiment revealed that the pre-existing body-centered cubic phase, which was mainly ferrite, was a minor deformation path, although ferrite was the major constituent phase.

Hierarchical Deformation Heterogeneity during Lüders Band Propagation in an Fe-5Mn-0.1C Medium Mn Steel Clarified through <i>in situ</i> Scanning Electron Microscopy

“…8(a), the Lüders front is observed in the upper region of the image. As reported in previous studies, 18,19) the Lüders front consists of multiple thin deformation bands. During the growth of the Lüders band, which is achieved by the propagation of the Lüders front, the following behaviors were observed:…”

“…These observations indicate that the initiation behavior of the thin deformation bands is dependent on the microstructure heterogeneity (presence of soft grains or grain groups) and surface geometry (roughness) of the side edges of the specimen, which is consistent with the discussion in the previous section. Based on the previous study, 18) austenite grains act as the soft grains during the Lüders deformation. It may be noteworthy that the solute carbon that concentrates in austenite is considered to harden the austenite grains significantly.…”

“…Specifically for a representative medium-Mn steel, for example, cold-rolled and well-intercritically annealed Fe-5Mn-0.1C steel, preferential plastic deformation occurs in austenite during the Lüders deformation. 18) The plasticity evolution in austenite occurs via deformation-induced martensitic transformation and dislocation slip. Furthermore, the distribution of the band evolution is discontinuous on a mesoscopic scale.…”

“…Furthermore, the distribution of the band evolution is discontinuous on a mesoscopic scale. 18,19) However, with regard to this hierarchical deformation heterogeneity during Lüders band propagation in medium manganese steels, there is a lack of clarity on the following aspects, which have been addressed in the present work:…”

“…The deformation bands are best visualized using back-scatter electron imaging (BSE). 18,19) Therefore, to study the plasticity evolution, which is hierarchical and heterogeneous, in-situ scanning electron microscopy (SEM) coupled with BSE has been performed at different scales.…”