Formation of the Fine Structure of Pearlite Steel under Ultra-long Plastic Deformation

By the methods of transmission electron microscopy, the quantitative transformations of a structure at depths of 0, 2, 5, and 10 mm along a central axis and the axis of symmetry of a head fillet of lengthy differentially quenched rails after a severe plastic deformation (passed tonnage 1770 million tons of gross weight) are revealed on the micro- and nanoscale levels. On the microscale level, the transformation of a pearlite colony by cutting cementite plates with moving dislocations and subsequent dissolution with the escape of carbon to dislocation lines, low- and large angle boundaries are established. On the nanoscale level, the subgrain structure, being formed in surface layers, contains nanodimensional cementite particles, located at dislocations, in junctions and along the subgrain boundaries. The formation of the subgrain structure is the result of dynamic recrystallization under megaplastic deformation realized in the process of extremely long operation of rails. The formation of so-called "channels of deformation" is detected.