Fragmentation of the grain structure of quenched rails

Transmission electron microscopy permits layer-by-layer structural analysis (along the central axis and in the direction of the rounded corner) of bulk-quenched and differentially quenched rails at distances of 0, 2, and 10 mm from the working surface. Regardless of the direction and the distance from the working surface, the structure of all the rails consists of plate-pearlite grains and ferrite grains, containing cementite particles of different shape (ferrite–carbide mixture) and grains of structure-free ferrite (ferrite grains that do not contain carbide phase, grain-boundary ferrite). The morphology and defect substructure of the phases are studied; the locations of the stress concentrators are established. Formulas are derived for the fragmentation parameters of the grains in the ferrite–carbide mixture as a function of the heat-treatment conditions and the distance from the working surface.