ИСТИНА

Cementite, which exists as a disperse phase in carbon steels, strongly affects their mechanical and magnetic properties. Doping elements of steel can also enter the cementite lattice, thus changing the size, shape, and properties of the cementite particles and of the steel also. In particular, nickel, which in itself is not a carbide- forming element, when using in a steel to improve its mechanical properties, was shown to enter the cementite lattice as an iron-substituting element and to change its magnetic properties [1]. In [2-4], cementite with nickel or/and chromium was obtained by mechanical alloying and subsequent thorough annealing. Mechanical alloying allows one to produce nonequilibrium metastable compounds, in particular to obtain samples with a high content of cementite (up to 95–100% [3]). The samples with 0 - 20 % of iron replaced by Ni/Cr were studied in [2-4] by X-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. In this work, we have performed first-principles calculations of electron structure of cementite with Ni and Cr replacing iron atoms with concentration close to that in [2-4], to acquire additional information on local structure of samples and hyperfine parameters. The unit cells were fully relaxed through finding the minimum of total energy over the lattice parameters and atomic positions. The obtained data for magnetization, atomic magnetic moments, and parameters of hyperfine interaction at Fe nuclei are compared with those for pure cementite and used to interpret experimental magnetic and Mössbauer data. This study was performed within the scope of the State Task (no. АААА-А17-117022250038-7) and was partly supported by the Program of Ural Branch of the Russian Academy of Sciences (project no. 18-10-2-21).