Structure, Phase Composition, and Defective Substructure of Rails of the Highest Quality Grade

Analysis of structure-phase states in-a-bulk hardened and a head-hardened rails

“…By TEM methods it is shown [3,4] that irrespective of the mode of heat treatment, a polycrystalline structure is formed in the surface layer of samples about 10 mm thick represented by pearlite grains of lamellar morphology (eutectoid mixture of ferrite and cementite in which both phases are in the form of extended lamellas) ( Fig. 2(a)), ferrite grains in which cementite particles of spherical, globular, and lamellar shapes are observed (in the text below referred to as ferrite-carbide mixture grains) ( Fig.…”

“…Examination of the relative content of the given structural components and the dispersity of the pearlite structure (evaluated by an average value of interlamellar distance) shows that after bulk hardening the structure is more homogeneous (as compared to the structure of steel formed as a result of head hardening) in the near-surface layer of steel (a layer about 2 mm thick) and is less homogeneous in the layer at the distance of about 10 mm from the running surface (Table 2). Earlier it was noted [3,4] that electron microscope images of structure of the rail steel samples examined practically always (it is not dependent on a category of rails and a hardening mode) contain bend extinction contours. Availability of bend extinction contours in the electron microscope images denotes lattice bending with torsion of the given region of the material, and, hence, the internal stress fields bending a thin foil [2].…”