ON THE GRAIN-GROWTH EXPONENT OF PURE IRON

Grain growth data on zone-refined iron were reanalyzed quantitatively to take into account the initial grain size and specimen thickness eff ect. The deviations from parabolic growth noted in an earlier analysis [Can. Metall. Q. 13, 275 (1974)] are attributed to the use of the app roximate Beck formula (lambda congruent-to K . t(n)) for grain growth kinetics which does not take these two important factors into account. Based on the new analysis, grain growth in zone-refined iron over the entire range of temperatures studied can be understood in terms of a single, thermally-activated rate process with an activation energy app roximately the same as that for lattice self-diffusion. Furthermore, i t is not necessary to invoke a non-linear velocity/driving force relat ionship to understand the kinetics. The high activation energy may be caused by an unknown impurity present in the iron which gave rise to a n impurity drag effect.