Effect of preheating/post-isothermal treatment temperature on microstructures and properties of cladding on U75V rail prepared by plasma cladding method

Rail cladding is a cost-effective approach for track maintenance and protection from rapid growth of mileage and Rolling Contact Fatigue (RCF) phenomenon. In this study, cladding layers are prepared on the surface of a U75V rail substrate using a plasma cladding approach with different substrate preheating temperatures. Preheating of the substrates creates an isothermal treatment for the cladding material after solidification of the molten pools. The effects of these post-solidification isothermal treatment temperatures (480°C, 340°C, and 200°C) on microstructures, mechanical properties and corrosion resistance are studied. The results indicate that the post-isothermal treating temperature affects the fractions of granular bainite, upper bainite, lower bainite, martensite and M/A island in the microstructure. The hardness of cladding layers is higher than that of the U75V substrate, and slightly increases as the pretreating temperature decreases. The specimen prepared at 340 °C has the highest tensile strength, which is 14.5% higher than the U75V rail. The interface between the cladding layer and the substrate also processes a strong bonding with the bonding strength of 789 MPa. Based on the comprehensive performance, the post-isothermal treating temperature of 340 °C is most suitable for cladding on the U75V rail. The plasma cladding process followed by post-isothermal treatment proves to be a flexible and effective approach to manipulate the microstructure of the cladding and restore the properties of the rail substrate.