Fine structure formation in rails under ultra long-term operation

By the methods of transmission electron microscopy (TEM) at micro-and nanoscale levels the quantitative transformations of structure at a depth of 0, 2, 5, 10 mm along central axis and symmetry axis of fillet head of lengthy differentially quenched rails after severe plastic deformation (passed tonnage of 1770 mln. gross tons) are revealed. At a microscale level the transformation of cementite plates by newly formed grain boundaries absorption of carbon atoms from bulk carbides is established. At a nanoscale level the subgrain structure, being formed in surface layers, contains cementite nanodimensional particles, localized in junctions and along subgrain boundaries. This type of structure was formed as a result of dynamic recrystallization under megaplastic deformation being realized in a process of extremely long-term service of rails. The formation of so-called 'channels of deformation' is determined. It is shown that scalar and excess dislocation density in ferrite constituent of steel structure increases as the rail head surface is approached.

Automated summary

The study reveals quantitative transformations of structure in the fillet head of lengthy differentially quenched rails after severe plastic deformation using transmission electron microscopy (TEM) at micro- and nanoscale levels. The formation of specific subgrain structure and cementite particles in the surface layers of rails after long-term service is demonstrated.