Revisiting the formation mechanism of intragranular κ-carbide in austenite of a Fe-Mn-Al-Cr-C low-density steel - Université de Lille
Article Dans Une Revue Scripta Materialia Année : 2021

Revisiting the formation mechanism of intragranular κ-carbide in austenite of a Fe-Mn-Al-Cr-C low-density steel

Résumé

It was usually believed that the formation of intragranular κ-carbide in γ-austenite was attributed to spinodal decomposition followed by ordering reaction. In this work, near-atomic scale characterization of an austenite-based Fe-20Mn-9Al-3Cr-1.2C (wt. %) low-density steel, using (high-resolution) scanning transmission electron microscopy and atomic probe tomography, reveals that the initially-formed κ-carbides (2-3 nm in particle size) are featured with an ordered L′1 2 structure but without detectable chemical partitioning. Further, the Gibbs energy of the FCC phase obtained by thermodynamic calculations always shows a positive curvature (i.e. < 0) with the variable contents of Al and C in the temperature range 400-800 °C. Both the results demonstrate that the ordered nuclei of κ-carbide can form directly in the disordered γ-austenite rather than through the well-known spinodal decomposition-ordering mechanism. The extremely low nucleation barrier is due to the similar lattice structure, same composition and complete coherency between the γ-austenite matrix and κ-carbides.
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Dates et versions

hal-03323667 , version 1 (22-08-2021)

Identifiants

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Jianlei Zhang, Yueshan Jiang, Weisen Zheng, Yuxiang Liu, Ahmed Addad, et al.. Revisiting the formation mechanism of intragranular κ-carbide in austenite of a Fe-Mn-Al-Cr-C low-density steel. Scripta Materialia, 2021, Scripta Materialia, 199, pp.113836. ⟨10.1016/j.scriptamat.2021.113836⟩. ⟨hal-03323667⟩
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