Thermal Cycle–Microstructure–Property Relationships in Rail Steel Heat‐Affected Zone Simulated by Gleeble

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Abstract
This study investigates the microstructural evolution and mechanical response of premium rail steel subjected to heat‐affected zone (HAZ) thermal cycles representative of flash butt welding (FBW). Dilatometry experiments were performed using a Gleeble thermomechanical simulator. Samples were austenitized at 1100 °C (100 °C/s, 60 s dwell) and cooled at 1–8 °C/s. Cooling rates of 1–3 °C/s produced predominantly pearlitic microstructures, whereas higher rates promoted bainite and martensite formation. HAZ physical simulations were then conducted at peak temperatures of 1200, 1060, 900, and 750 °C. Fully pearlitic microstructures developed at 1060 and 900 °C, while 750 °C produced spheroidized pearlite. The spheroidized condition exhibited the lowest tensile strength (737 MPa) and hardness (296 HV), whereas 1060 °C yielded the highest values (864 MPa and 418 HV). Optical microscopy, scanning electron microscopy, and electron backscatter diffraction revealed systematic changes in colony morphology, grain structure, and crystallographic characteristics. The 750 °C condition showed the lowest hardness and highest wear rate, while 1200 °C exhibited the highest nanohardness and wear resistance, but greater microstructural heterogeneity and reduced ductility. These findings demonstrate the strong influence of HAZ thermal history on phase transformation and mechanical performance, providing guidance for optimizing FBW parameters in rail steels.

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