  High temperature atomic configurations of fcc Fe-Cr-Ni alloys with alloy
composition close to austenitic steel are studied in statistical thermodynamic
simulations with effective interactions obtained in ab initio calculations. The
latter are done taking longitudinal spin fluctuations (LSF) into consideration
within a quasiclassical phenomenological model. It is demonstrated that
magnetic state affects greatly the alloy properties and in particular, it is
shown that the LSF substantially modify the bonding and interatomic
interactions of fcc Fe-Cr-Ni alloys even at ambient conditions. The calculated
atomic short-range order (SRO) is in reasonable agreement with existing
experimental data for Fe0.56}Cr0.21Ni0.23, which has strong preference for the
(001) type ordering between Ni and Cr atoms. A similar ordering tendency is
found for the Fe0.75Cr0.17Ni0.08 alloy composition, which approximately
corresponds to the widely used 304 and 316 austenitic steel grades.
