Modeling the effect of prior austenite grain size on bainite formation kinetics

Daniel dos Santos Avila*, S. Erik Offerman, Maria J. Santofimia

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

While experiments show that refining the prior austenite grain size can either accelerate or decelerate bainite formation in steels, kinetic models based on the successive nucleation of bainitic ferrite subunits can only predict an acceleration. In this work we develop a physically-based model for bainite kinetics assuming a displacive growth mechanism which is able to reproduce both faster and slower bainite formation kinetics induced by austenite grain refinement. A theoretical analysis of the model and comparison against published experimental data show that slower kinetics for smaller grains is favored as the difference between the activation energy for grain boundary and autocatalytic nucleation of bainite increases, and as the austenite grain refinement results in finer bainite sub-units. We also theoretically analyze the density of initially present potential nucleation sites for bainite and show that the values of density used in other published bainite nucleation models are mostly underestimated. After using physically consistent values for the density of potential nucleation sites, we were able to calculate the apparent lengthening rate of bainite sheaves which were in line with experimentally measured lengthening rates.

Original languageEnglish
Article number119656
Number of pages14
JournalActa Materialia
Volume266
DOIs
Publication statusPublished - 2024

Funding

This project has received funding from the Research Fund for Coal and Steel under grant agreement No 899521 . We would also like to acknowledge all of our partners in the RFCS-funded project MartBain, and in particular Dr. Stefan van Bohemen, Dr. Carlos Garcia-Mateo, Dr. Thomas Sourmail, and Dr. Johaness Moeller for the fruitful discussions during our meetings.

Keywords

  • Bainite
  • grain size
  • nucleation
  • phase transformation kinetics
  • theory and modeling

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