Regional Thermal Cycles, Microstructure, and Local Mechanical Properties of U75V Rail Joints Produced by Electroslag Welding

Rails are critical load-bearing components in railway transportation systems, and the quality of their welded joints is essential to operational safety. However, the large variation in rail cross-sectional geometry makes it difficult to achieve suitable thermal cycles throughout the rail base, web, and head using a uniform welding heat input. In this study, a region-specific electroslag welding strategy was developed for U75V rail, in which the rail base was welded simultaneously using three wires, while the rail web and head were welded using a single wire. Under this region-specific welding configuration, the calculated t8/5 values were 101.4, 73.6, and 62.5 s in the rail base, web, and head, respectively. Representative microstructural observations showed lamellar pearlite as a major constituent at the examined locations in all three regions. From the rail base to the head, the EBSD orientation-domain size decreased from 15.6 to 7.6 μm, and the pearlite interlamellar spacing decreased from 158.9 to 110.3 nm. These microstructural variations were accompanied by an increase in the local weld-metal ultimate tensile strength from 1130.7 to 1180.6 MPa and in hardness from approximately 33 to 36 HRC. The results reveal clear associations among the region-specific welding conditions, thermal histories, microstructural characteristics, and local mechanical properties.