Three-dimensional neutron depolarization experiments have been performed in
order to study the isothermal phase transformation from austenite (gamma-F
e) into ferrite (alpha-Fe) in medium-carbon steel. The polarization rotatio
n during transmission through the sample is a measure of the ferromagnetic
ferrite fraction, while the degree of depolarization determines the charact
eristic length scale of the ferrite microstructure. The application of a ni
ckel coating is found to suppress ferrite formation at the surface, which a
llows for a direct analysis of the bulk transformation kinetics. (C) 2000 E
lsevier Science B.V. All rights reserved.