  High energy x-ray diffraction microscopy was used to image the microstructure
of $\alpha$-Fe before and after a 600 $^\circ$C anneal. These data were used to
determine the areas, curvatures, energies, and velocities of approximately
40,000 grain boundaries. The measured grain boundary properties depend on the
five macroscopic grain boundary parameters. The velocities are not correlated
with the product of the mean boundary curvature and grain boundary energy,
usually assumed to be the driving force. Boundary migration is made up of area
changes (lateral motion) and translation (normal motion) and both contribute to
the total migration. Through the lateral motion component of the migration, low
energy boundaries tend to expand in area while high energy boundaries shrink,
reducing the average energy through grain boundary replacement. The driving
force for this process is not related to curvature and might disrupt the
expected curvature-velocity relationship.
