Evaluation of fatigue fracture mechanism in a flash butt welding joint of a U75V type steel for railroad applications

• The upset pressure of influencing flash welding joint quality was studied.
• We study the corrosion-fatigue properties of flash welding joint.
• We report the fatigue fracture mechanism of U75V rail steel flash welding joint.

Nowadays, U75V steel is widely used in high speed railway construction, and commonly jointed by means of flash butt welding procedure. Considering the fact that fatigue failure is the main failure mode of railways, to ensure an adequate service life of railways, especially railways in coastal areas, this work mainly investigated the fatigue fracture mechanism of flash butt welding joints of U75V rail steel. First, the flash butt welding joints were prepared under two sets of process parameters and certain welding joints were corroded beforehand. Then, the microstructure, hardness, S–N curve and fatigue fracture of welding joints were analyzed in detail. Finally, the fracture mechanism was comprehensively discussed by considering the effect of welding parameters. It was concluded that the fatigue performance of flash welding joint is mainly determined by the upset pressure. Higher upset pressure is conducive to improve the fatigue strength. The fatigue crack source of fractured specimens under the condition of corrosion environment is at interface area and at the subsurface of sample. Meanwhile, the corrosion fatigue life obviously reduces.