Research of fatigue strength of welded joints of rails

In order to confirm the efficiency of various versions of the modernized design of the rail quench cooling system sprayer, a study of the structure of the hardened layer, structural and fatigue strength of welded rail joints after various heat treatment methods was conducted. In order to confirm the results of hardness measurements on rails of three batches (I, II, III) and the results of static tests of batches II and III, templates were cut out and metallographic examination was carried out. Analysis of the presented microstructures in the rail head shows that the microstructure in the head is quenched sorbite. The microstructure in the rail neck is pearlite partially with a globular form of cementite, in the rail foot it is represented by sorbite-like pearlite, which is associated with cooling the foot in air. In this case, a pearlite microstructure is formed on the feet of the foot. The microstructure study on samples II and III was carried out at a distance of 5–10 mm from the welded joint after induction heat treatment. The microstructure in the rail head II in the central zone is represented by a sorbitic structure with a ferrite network, in the rail neck – by sorbitol of mixed morphology (lamellar and granular), in the base zone in the middle and feathers – by a structure of sorbitic pearlite, mixed morphology (lamellar and granular). The microstructure along the axis of the rail head III is represented by a sorbitic structure, in the neck – by a mixed morphology of sorbite (mixed and granular, the rail foot in the middle is troostite and troostosorbite. The microstructure of the foot feather consists of troostosorbite. The results of testing welded joints under three-point bending of rail samples are presented. As a result of the analysis, it was found that the indicators for the destructive load and deflection are higher when using a two-way compressed air supply system in the cooling sprayer. When testing samples, the load was applied to the head (in the stretch zone of the foot), the characteristics of fatigue tests were determined. The number of cycles cumulatively increased by 669 thousand with two-sided hardening, and destructive stresses by 9.5%.