Exploring bainite formation kinetics distinguishing grain-boundary and autocatalytic nucleation in high and low-Si steels

Exploring bainite formation kinetics distinguishing grain-boundary and autocatalytic nucleation in high and low-Si steels

Ravi, A.M.
Sietsma, J.
Santofimia, M.J.

Mechanical, Maritime and Materials Engineering

Materials Science and Engineering

2016-02-15

Bainite formation in steels begins with nucleation of bainitic ferrite at austenite grain boundaries (?/? interfaces). This leads to creation of bainitic ferrite/austenite interfaces (?/? interfaces). Bainite formation continues through autocatalysis with nucleation of bainitic ferrite at these newly created ?/? interfaces. The displacive theory of bainite formation suggests that the formation of bainitic ferrite is accompanied by carbon enrichment of surrounding austenite. This carbon enrichment generally leads to carbide precipitation unless such a reaction is thermodynamically or kinetically unfavourable. Each bainitic ferrite nucleation event is governed by an activation energy. Depending upon the interface at which nucleation occurs, a specific activation energy would be related to a specific nucleation mechanism. On the basis of this concept, a model has been developed to understand the kinetics of bainite formation during isothermal treatments. This model is derived under the assumptions of displacive mechanism of bainite formation. The fitting parameters used in this model are physical entities related to nucleation and microstructural dimensions. The model is designed in such a way that the carbon redistribution during bainite formation is accounted for, leading to prediction of transformation kinetics both with and without of carbide precipitation during bainite formation. Furthermore, the model is validated using two different sets of kinetic data published in the literature.

http://resolver.tudelft.nl/uuid:5122df42-e599-4b45-9253-1ccf9bd1f585

Elsevier

1359-6454

https://doi.org/10.1016/j.actamat.2015.11.044

Acta Materialia, 105, 2016

Institutional Repository

journal article

© 2015 Acta Materialia Inc.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)