Rolling Wear and Damage Properties of Three Kinds of Pearlite Rail Welded Joints

High-speed passenger transport and heavy haul freight transportation have gradually become the development direction of railway transportation. As one of the weakest parts in the track structure, the damage of rail welded joints increases rapidly, the cost of line maintenance increases greatly, and even affects the safety of train operation. The wear and damage of rail welded joints are related to their microstructure. The microstructure and mechanical properties of each region on the rail welded joints of three different pearlite materials were studied. In this study, the MJP-30A tester was used to carry out rolling sliding wear experiments of the materials at the joints. This machine allowed two discs to run against each other with controlled normal and tangential forces to simulate the rolling-sliding contact between wheel and rail. The experiments were carried out under dry conditions and at the room temperature, and simulated axle load was 25 t. The contact stress was calculated to be 1 215 MPa by Hertz contact theory. The wheel speed was 500 r/min, the rail speed was 495 r/min, and the creep rate was 1%, and the number of cycles was 100 000 cycles. Each group was repeated during the test. During the test, the wear and damage characteristics of the joints were studied from the aspects the hardness values, the microstructure, the adhesion coefficient, the wear rate, the macro morphology of the wear surface and the profile damage. The results showed that the fusion line in the center of the weld was a white bright area under the optical microscope. As the carbon content of the three welded joints decreased, the pearlite lamellar spacing increased, the content of pro-eutectoid ferrite increased, resulting in a decrease in hardness. The hardness of the three welded joints was low at the center of the weld, the microstructure of the heat affected zone was refined, and the hardness was increased. The wear rate decreased with the increase of average hardness, and the surface damage of the weld zone was more serious than that of the heat affected zone. The surface damage at the rail weld was characterized by large spalling. Compared with the weld zone, the surface cracks in the heat affected zone were short and the number increased, mainly manifested as ratchet failure and slight peeling. The plastic deformation layer of the weld zone was bigger than that of the heat affected zone, which was about 12%~15% thicker. The plastic deformation of rail 2# was the most serious, and the thickness was 286 μm in the weld zone. In the heat affected zone, the thickness was 243 μm. The fatigue cracks in the weld zone were characterized by multi-layer cracks, and different degrees of breakage occurred inside the material. The heat affected zone showed short and shallow single cracks. The crack length and depth of the weld zone awere larger than that of the heat affected zone, and the crack angle was smaller than that of the heat affected zone. In the weld zone, the average crack length and crack depth of rail 2# were the biggest, reaching 317.1 μm and 23.6 μm, respectively. The fatigue crack was in line with the plastic deformation. With the increase of pearlite lamellar spacing, the damage degree of rail increased firstly and then decreased, and the crack angle decreased. With the increase of pearlite lamellar spacing, the degree of rail damage increased sharply and then decreased slightly, and the crack angle decreased. The pearlite lamellar spacing of rail 1# was the smallest and the damage degree was the smallest. The pearlite lamellar spacing of rail 3# was bigger than that of rail 2#, but the damage degree was reduced. With the increase of the interlayer spacing, the resistance of the crack in the rail decreased, which made it easier to expand, and it was also easier to break and remove, so the wear rate increased and the damage was reduced. Based on the above results, it could be found that the rolling wear and contact fatigue behavior of the welded and the heat affected zone of the welded joints of different materials were consistent. The hardness of the welded center was lower than that of the heat affected zone, and the damage and plastic deformation of the welded were more serious than that of the heat affected zone. The text results could provide a theoretical basis for improving the welded process and improving the welded joint performance.