Optimization of stress-relief heat treatment for overlay weld repair of severely used rail tracks: effects on residual stress, microstructure and wear resistance

Abstract This study investigates the optimization of stress-relief heat treatment for overlay weld repair of severely used rail tracks. The research focuses on 900A rail steel samples that have been in service for over 20 years, exhibiting significant wear and plastic deformation. Pre-welding heat treatments at 300 °C, 400 °C, and 500 °C were applied to reduce service-induced residual stresses before flux core arc welding (FCAW) repair using high-Mn filler material. The effects of these treatments on residual stress distribution, microstructure, hardness, and wear resistance were systematically analyzed. Scanning electron microscopy (SEM), X-ray residual stress analysis, microhardness testing, and pin-on-disc wear tests were employed to characterize the samples. Results indicate that stress relief at 300 °C and 400 °C effectively reduces residual stress while maintaining or enhancing hardness and wear resistance. However, treatment at 500 °C led to over-tempering, resulting in decreased hardness and increased wear rates. The 400 °C treatment emerged as the optimal temperature, providing a balanced combination of reduced residual stress, favorable microstructure, and improved mechanical properties across all welded zones.