Evolution of the Lamellar Pearlite Structure of Rail Steel under Tension

Methods of modern physical materials science were used to investigate the mechanical properties of rail steel, the defective substructure of pearlite with lamellar morphology, and the fracture surface of rail steel subjected to fracture under uniaxial tensile strain. The ultimate strength was found to vary from 1247 to 1335 MPa and the fracture strain of the specimens to range from 0.22 to 0.26. The deformation of steel is shown to be coupled with the division of ferrite plates into fragments by low-angle boundaries along with a significant increase in the scalar dislocation density up to 7.9 × 1010 cm–2 (the scalar dislocation density of original rail steel being 3.2 × 1010 cm–2). In addition, internal stress fields arise in the form of bend extinction contours. Sources of the stress fields are identified. It was found that cementite plates were fractured by cutting and dissolution with subsequent transfer of carbon by moving dislocations to ferrite plates to form there nanosized (8.3 nm) round particles of tertiary cementite. It is shown that the dissolution of cementite plates is accompanied by fragmentation (division into coherent scattering regions of 9.3 nm on average).