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

Authors
  • Zhang, Jianlei
  • Jiang, Yueshan
  • Zheng, Weisen
  • Liu, Yuxiang
  • Addad, Ahmed
  • Ji, Gang
  • Song, Changjiang
  • Zhai, Qijie
Publication Date
Jul 01, 2021
Identifiers
DOI: 10.1016/j.scriptamat.2021.113836
OAI: oai:HAL:hal-03167683v1
Source
HAL-INRIA
Keywords
Language
English
License
Unknown
External links

Abstract

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′12 structure but without detectable chemical partitioning. The Gibbs energy of the FCC phase obtained by thermodynamic calculations always shows a positive curvature (i.e. d2g/dx2< 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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