CHEN, Hao; BORGENSTAM, Annika; ODQVIST, Joakim; ZUAZO, Iam; GOUNÉ, Mohamed; ÅGREN, John; VAN DER ZWAAG, Sybrand

doi:10.1016/j.actamat.2013.04.020

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CHEN, Hao
Faculty of Aerospace Engineering [Delft]

BORGENSTAM, Annika
KTH Royal Institute of Technology [Stockholm] [KTH]

ODQVIST, Joakim
KTH Royal Institute of Technology [Stockholm] [KTH]

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Acta Materialia. 2013, vol. 61, n° 12, p. 4512-4523

Elsevier

Résumé en anglais

New interrupted cooling experiments have been designed to study the kinetics of bainitic ferrite formation starting from a mixture of austenite and bainitic ferrite. It is found that the kinetics of bainitic ferrite formation during the cooling stage is determined by the isothermal holding time. The formation rate of bainitic ferrite at the beginning of the cooling decreases with increasing prior isothermal holding time. An unexpected stagnant stage during the cooling stage appears when the isothermal holding time increases to a critical point. There are two reasons for the occurrence of the stagnant stage: (i) a solute spike in front of the interface; and (ii) kinetic transition. A so-called Gibbs energy balance approach, in which the dissipation of Gibbs energy due to diffusion inside the interface and interface friction is assumed to be equal to the available chemical driving force, is applied to theoretically explain the stagnant stage. A kinetics transition from a fast growth mode without diffusion of Mn and Si inside the austenite-bainitic ferrite interfaces to a slow growth mode with diffusion inside the interface is predicted. The stagnant stage is caused by the transition to a slow growth mode. The Gibbs energy balance approach describes the experimental observations very well.< Réduire

Mots clés en anglais

Solute drag

Austenite

Bainitic ferrite

Interface migration

Transformation kinetics

Dissipation of gibbs energy

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Application of interrupted cooling experiments to study the mechanism of bainitic ferrite formation in steels

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