Formation of microscopic internal stresses in rails during long-term operation

The level of microscopic internal long-range stress fields al on the rolling surface and the working fillet is determined for two categories of rails with a carbon content of 0.74 wt. % and 0.91 wt. %. DT350 for general purpose and DT400IK of increased wear resistance and contact endurance after the passed tonnage of 1,770 mln. t (for DT350) and 187 mln. t DT400IK (1) and 234 mln. t of DT400IK (2). For this purpose, the bending extinction contours were analyzed by means of transmission electron diffraction microscopy, the parameters of which were used in calculating al. The presence of excess extinction contours indicates the bending-torsion of the lattice, which is characterized by the excess density of dislocations. A comparison is made with other methods for measuring internal stress fields at the meso- and macro levels. It is shown that the parameters of the bending extinction contours are the most informative and allow one to control the locality of the measurement al. Sources of internal stress fields in rail steels are noted. An increase in the level of al was revealed in DT400IK rails in comparison with DT350 rails. The growth of the passed tonnage for rails of category DT400IK leads to an increase in al, the values of internal stresses on the fillet surface exceed the corresponding values on the rolling surface. The physical causes of the observed changes are discussed.