DOI: 10.20935/acadmatsci8461 ISSN: 2997-2027

Ordered B2 strengthening in low-density Fe-Mn-Al-Ni-C steels: a critical review

Mainak Saha
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Low-density Fe-Mn-Al-Ni-C steels strengthened by ordered B2 precipitates have attracted attention because they offer reduced density, high specific strength and promising strain-hardening capacity. This critical review examines how alloy chemistry, thermomechanical processing, B2 morphology, volume fraction, spacing and face-centered cubic (FCC)/B2 interface structure govern the macroscopic and micromechanical response of these steels. Particular emphasis is placed on reconciling apparently different interpretations of strain hardening, including short-range-ordering-assisted planar slip in the FCC matrix and back-stress hardening caused by strain incompatibility between the FCC and B2 phases. The review also evaluates the limitations of using Orowan-type strengthening models without complete information on interface structure and misfit strain, discusses the present lack of validated thermodynamic and mobility databases, and identifies unresolved industrial issues including scalable processing, additive manufacturing, weldability, fatigue, hydrogen embrittlement and corrosion. Finally, a correlative microscopy workflow combining characterization techniques such as electron backscattered diffraction, transmission Kikuchi diffraction, scanning transmission electron microscopy and atom probe tomography, and deformation experiments is proposed for resolving nanoscale B2 chemistry, ordering and deformation mechanisms.

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