Unraveling the effects of Nb interface segregation on ferrite transformation kinetics in low carbon steels

Haokai Dong, Yongjie Zhang, Goro Miyamoto, Masahiro Inomoto, Hao Chen, Zhigang Yang, Tadashi Furuhara

Research output: Contribution to journalArticlepeer-review

Abstract

Addition of small amount of Nb can strongly retard the ferrite growth kinetics. The origin has been attributed to the solute drag effect (SDE) by Nb segregation at the migrating ferrite/austenite interface. However, due to limitation of characterization techniques, the relations between elemental segregation, SDE and interface velocity have not been quantitatively clarified yet. Meanwhile, the strong affinity between Nb and C atoms can induce carbide precipitation at the interface, namely interphase precipitation, which may influence the Nb segregation behavior and make the issue even more complicated. Therefore, in this study, the interface information including amount of Nb segregation, energy dissipation, NbC precipitates and interface velocity in Fe-0.08C-(0.035, 0.061)Nb (mass%) model alloys is quantitatively investigated. It reveals that the energy dissipation at the migrating ferrite/austenite interface decreases with longer holding time or higher transformation temperature. The Nb atoms prefer to segregate at the non K-S interface rather than the near K-S interface. Amount of Nb segregation at the non K-S interface increases with longer time, while raising bulk Nb content or lowering transformation temperature does not lead to a notable increment of segregation. The relations between Nb segregation, energy dissipation, and interface velocity can be well reproduced by the SDE model with optimized parameters (i.e., segregation energy, interface thickness and trans-interface diffusivity). Occurrence of NbC interphase precipitation affects the transformation kinetics indirectly by weakening the SDE via consumption of Nb solutes in ferrite. In contrast, their pinning effect plays a marginal role.

Original languageEnglish
Article number117081
JournalActa Materialia
Volume215
DOIs
Publication statusPublished - 2021 Aug 15

Keywords

  • Energy dissipation
  • Ferrite growth
  • Interface segregation
  • Interphase precipitation
  • Solute drag effect

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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