Measurements of conduction electron spin resonance, temperature-dependent magnetization, small angle neutron scattering, and transmission electron microscopy were used for the analysis of chemical nonhomogeneity in austenitic steels with carbon + nitrogen or carbon only. It is shown that all studied steels are characterized by a nonhomogeneous distribution of alloying elements on the fine scale: from 3 to 5 nm in CrMnCN steels to about 30 nm in MnC Hadfield type steel. In the CN steels, their chemical homogeneity is improved by decreasing the C/N ratio. A ferromagnetic-type temperature behavior is observed in the CN steels at temperatures below 86 K, which is attributed to the blocking of magnetic moments of superparamagnetic clusters. The short-range decomposition of all studied steels results in a different splitting of dislocations, which corresponds to two different values of the stacking fault energy.