It was found that the data for 450 to 600C could be described by:

D (cm2/s) = 2.5 x 10-3 exp[-6.4(kcal/mol)/RT]

K.Niwa, M.Shimoji, S.Kado, Y.Watanabe, T.Yokokawa: Journal of Metals, 1957, 9, 96-101