TY - JOUR
T1 - In Situ 3D Neutron Depolarization Study of the Transformation Kinetics and Grain Size Evolution During Cyclic Partial Austenite-Ferrite Phase Transformations in Fe-C-Mn Steels
AU - Fang, H.
AU - van der Zwaag, S.
AU - van Dijk, N. H.
PY - 2018
Y1 - 2018
N2 - We have analyzed the evolution of the ferrite fraction and average ferrite grain size during partial cyclic austenite-to-ferrite and ferrite-to-austenite phase transformations in an Fe-0.25C-2.1Mn (wt pct) steel using three-dimensional neutron depolarization (3DND). In the 3DND experiments, the ferrite fraction is derived from the rotation angle of the neutron polarization vector, and the average grain size is determined from the shortening of the polarization vector. From these, the number density of ferrite grains is derived, which indicates that grain nucleation is negligible during partial cycling in the intercritical regime and that all transformation kinetics can be attributed to growth processes only. In the multiple successive cyclic partial transformations, the interfacial migration rate was found to be sluggish due to Mn partitioning. The transformation kinetics determined with 3DND was compared to the predicted behaviors for diffusion-controlled simulations under local equilibrium and para-equilibrium interfacial conditions. It was found that the simulation predictions under local equilibrium only qualitatively capture the transformation kinetic with a difference of one order of magnitude in the variation in the ferrite fraction during cycling. The cyclic behavior of this Fe-0.25C-2.1Mn (wt pct) steel shows that the austenite-ferrite interface indeed migrates back and forth during cycling, while at the same time, there is a gradual increase in both the ferrite fraction and the average ferrite grain size over subsequent cycles. The intrinsic cyclic behavior is only visible after subtracting the effect of the progressive interfacial migration into austenite. The present study demonstrates the advantage of 3DND in studying partial cyclic phase transformations over conventional experimental approaches.
AB - We have analyzed the evolution of the ferrite fraction and average ferrite grain size during partial cyclic austenite-to-ferrite and ferrite-to-austenite phase transformations in an Fe-0.25C-2.1Mn (wt pct) steel using three-dimensional neutron depolarization (3DND). In the 3DND experiments, the ferrite fraction is derived from the rotation angle of the neutron polarization vector, and the average grain size is determined from the shortening of the polarization vector. From these, the number density of ferrite grains is derived, which indicates that grain nucleation is negligible during partial cycling in the intercritical regime and that all transformation kinetics can be attributed to growth processes only. In the multiple successive cyclic partial transformations, the interfacial migration rate was found to be sluggish due to Mn partitioning. The transformation kinetics determined with 3DND was compared to the predicted behaviors for diffusion-controlled simulations under local equilibrium and para-equilibrium interfacial conditions. It was found that the simulation predictions under local equilibrium only qualitatively capture the transformation kinetic with a difference of one order of magnitude in the variation in the ferrite fraction during cycling. The cyclic behavior of this Fe-0.25C-2.1Mn (wt pct) steel shows that the austenite-ferrite interface indeed migrates back and forth during cycling, while at the same time, there is a gradual increase in both the ferrite fraction and the average ferrite grain size over subsequent cycles. The intrinsic cyclic behavior is only visible after subtracting the effect of the progressive interfacial migration into austenite. The present study demonstrates the advantage of 3DND in studying partial cyclic phase transformations over conventional experimental approaches.
UR - http://www.scopus.com/inward/record.url?scp=85053674504&partnerID=8YFLogxK
UR - http://resolver.tudelft.nl/uuid:7b952fe5-c33c-4cb0-bf62-0d8c7b470762
U2 - 10.1007/s11661-018-4905-8
DO - 10.1007/s11661-018-4905-8
M3 - Article
SN - 1073-5623
JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
ER -