  Applications of the M\"ossbauer spectroscopy (MS) in the investigation of
Fe-Cr alloys are reviewed. A high sensitivity of the hyperfine magnetic field
to the presence of Cr atoms in the vicinity of the probe Fe atoms permits
quantitative investigation of various aspects related both to the
crystallographic as well as to the magnetic phase diagram of this alloy system.
Concerning the former, presented is the relevance of MS for determining borders
of the miscibility gap and kinetics of the phase decomposition, distinguishing
between nucleation and growth and spinodal decomposition, identifying the
sigma-phase and studying kinetics of its precipitation. Regarding the magnetic
phase diagram, MS is useful for determining the Curie, the N\'eel and the
spin-freezing temperature, hence studying paramagnetic-ferromagnetic,
paramagnetic-antiferromagnetic and paramagnetic-spin-glass transitions. An
effect of different heat treatments, strain and irradiation with various
particles on a distribution of Cr atoms in the Fe matrix is demonstrated, too.
For bcc-FeCr alloys relevance of MS for determining changes in spin and charge
densities at Fe-sites induced by neighboring Cr atoms is illustrated, as well
as its usefulness in studying changes caused by a high-temperature sulphidation
and oxidation. Concerning properties of sigma-FeCr alloys the application of MS
for determining the Curie and Debye temperature is reviewed. Application of MS
to study an effect of magnetism on the lattice dynamics of Fe atoms in
sigma-FeCr is also exemplified. Last but not least, determining a magnetic
texture and mechanical alloying is addressed.
