Modelling study on the three-dimensional neutron depolarisation response of the evolving ferrite particle size distribution during the austenite–ferrite phase transformation in steels

Abstract

The magnetic configuration of a ferromagnetic system with mono-disperse and poly-disperse distribution of magnetic particles with inter-particle interactions has been computed. The analysis is general in nature and applies to all systems containing magnetically interacting particles in a non-magnetic matrix, but has been applied to steel microstructures, consisting of a paramagnetic austenite phase and a ferromagnetic ferrite phase, as formed during the austenite-to-ferrite phase transformation in low-alloyed steels. The characteristics of the computational microstructures are linked to the correlation function and determinant of depolarisation matrix, which can be experimentally obtained in three-dimensional neutron depolarisation (3DND). By tuning the parameters in the model used to generate the microstructure, we studied the effect of the (magnetic) particle size distribution on the 3DND parameters. It is found that the magnetic particle size derived from 3DND data matches the microstructural grain size over a wide range of volume fractions and grain size distributions. A relationship between the correlation function and the relative width of the particle size distribution was proposed to accurately account for the width of the size distribution. This evaluation shows that 3DND experiments can provide unique in situ information on the austenite-to-ferrite phase transformation in steels.

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

“…[18] The validity of the analysis was recently evaluated by simulated particle size distribution. [19] The influence of the particle size distribution was characterized in detail. The previous simulations confirm that Eq.…”

“…In a recent study, we computationally analyzed the effect of the size distribution on the 3DND-derived microstructural parameters and found that the 3DND method, under certain conditions, may even yield information on the ferrite grain size distribution. [19] Therefore, the 3DND technique provides a powerful tool to simultaneously measure the ferrite fraction and the grain size within the bulk of steel samples. This technique has been used successfully to study austenite-to-ferrite [20] and austenite-to-pearlite [21] phase transformations in steels under isothermal conditions and during continuous cooling conditions.…”