Silicon impact on carbon ordering at the martensite lattice: Molecular dynamics simulations

Abstract

Despite their widespread use in the industry, silicon-alloyed bainitic steels remain insufficiently studied in many respects. For instance, there is no available information on the impact of silicon impurities on the properties of martensitic structure. The present article deals with this issue. The results of a computer simulation of the impact of silicon impurities on the tetragonal distortion of martensite lattice and the interaction of carbon atoms in a body-centered cubic (bcc) lattice of iron using the molecular dynamics method are presented. Interatomic potentials that make it possible to describe the interactions of Fe-Si-C in martensite within the framework of the embedded atom model (EAM) are developed. It has been established that when silicon is added to steel, the lattice constant c decreases noticeably and the constant a increases slightly. The tetragonality expressed by c/a ratio decreases with respect to the results of Kurdyumov’s experiment for any carbon concentrations. The impact of silicon on the formation of martensite was studied by minimizing the energy of the strain-induced interaction parameter λ2(0) from the order-disorder transition theory in Zener-Khachaturyan interstitial solutions, which determines the critical temperature of the bcc-bct (body-centered tetragonal) transition. The calculations do not confirm the direct proportional dependence of the change in the tetragonality of martensite and the nature of carbon activity variation during alloying with silicon, which increases activity but decreases tetragonality.