  A redistribution of Cr atoms related to a phase decomposition (PD) caused by
an isothermal annealing at 415 C in a 15.15 at%Cr Fe-Cr alloy was studied in an
ex-situ way by the conversion electrons M\"ossbauer spectroscopy. Analysis of
the spectra in terms of a two-shell model enabled determination of
probabilities of 17 different atomic configurations and average numbers of Cr
atoms within the first (1NN) and the second (2NN) neighbor shells versus
annealing time, separately. The annealing-time evolution of these numbers,
expressed in terms of the Cowley-Warren short-range order (SRO) parameters, was
shown to follow the Johnson-Mehl-Avrami-Kolgomorov equation. The SRO-parameter
averaged over the 1NN-2NN shells was revealed to be linearly correlated with
the average hyperfine field. Signatures in favor of the nucleation and growth
mechanisms responsible for PD are discussed, too.
