REDISTRIBUTION OF CARBON IN THE STRUCTURE OF RAIL STEEL AFTER LONG-TERM OPERATION

Abstract

Carbon in the steel structure can be in a solid solution based on α- and γ-iron (at the position of interstitial elements), on dislocations (in the form of Cottrell and Maxwell atmospheres), on interphase (carbide/matrix) and intraphase (grain boundaries, packets and crystals of packet and lamellar martensite) boundaries, in carbide phase particles. The amount of carbon in solid solutions based on α- and γ-iron is usually estimated by the relative change in the crystal lattice parameter of these phases. The amount of carbon in carbide particles is estimated based on the chemical composition of the carbide, the type of crystal lattice and the volume fraction of carbide phase particles in steel. For cementite (assuming a stoichiometric composition), a similar calculation is performed in the work. Estimation of the amount of carbon located on defects (dislocations and interfaces) is the most difficult moment and is practically not amenable to direct experimental determination. The situation is resolved by using indirect methods, such as internal friction and micro X-ray spectral analysis, and theoretical assessments are also made. The most complete analysis of carbon redistribution in unalloyed steels depending on the tempering temperature is carried out in the work, in the case of alloyed steels (quenching and low-temperature tempering conditions) – in the works.