ИСТИНА

Cementite, which exists as a dispersed phase in a carbon steel, strongly affects its mechanical and magnetic properties. Alloying elements in a steel can also enter a lattice of cementite, thus, affecting size, form, and properties of the cementite particles. In particular Ni, which is used in steels for improving their mechanical properties and is not a carbide former, was shown [1] to enter the lattice of cementite and change its magnetic properties. In [2] cementite with Ni was obtained by mechanical alloying followed by a thorough annealing, the method being able to produce samples with a high content of cementite (up to 95-100 %) [3]. The samples obtained were studied in [2] by x-ray and magnetic measurements and Mossbauer spectroscopy. Interpretation of experiments and understanding the underlying processes is hindered by the fact that distribution of Ni in the samples was not uniform: the susceptibility curve showed two Curie temperatures at 220 and 240 degree C, both being a bit higher than that of pure cementite. So, the authors considered this as evidence of two types of cementite, namely, Ni-enriched and Ni-depleted cementite. In this work we have conducted first-principles calculations of electron structure of cementite with Ni replacing iron atoms with concentration close to that in [2]. The unit cell was fully relaxed through finding minimum of total energy over the lattice parameters and atomic positions. The calculated values of atomic magnetic moments, hyperfine parameters at Fe nuclei are used for interpretation of the magnetic and Mossbauer experimental data. Acknowledgements. This work was supported by the Ural Branch of Russian Academy of Sciences № 15-6-2-16.