Formation of Fine Surface of Long Rails on Differentiated Hardening

by methods of transmission electron diffraction microscopy the layer-by-layer analysis was carried out and quantitative parameters of structural phase states, dislocation substructure, internal stress fields and particles of carbide phase in the head of 100-meter rails along the central axis and along the fillet after differentiated hardening were revealed. It was shown that differentiated hardening forms a morphologically multi-aspect structure presented by grains of lamellar perlite, ferrite-carbide mixture and structurally free ferrite in surface layers up to 10 mm in depth. It was determined that the structure being formed has a gradient character. The state of surface layer depends on direction of study (along central axis and along the fillet) and depth of occurrence of the layer under study. It was detected that relative content of structurally free ferrite grains and ferrite-carbide mixture grains decrease when distance from rail surface increases. The facts revealed as a result of the studies performed testify to a higher cooling rate of fillet surface with respect to surface material located along the central axis.