Quasi-equal strength and toughness matching rail steel joint obtained via friction welding below Ac1 temperature

Abstract

U75V rail steel rods underwent continuous-drive friction welding (CDFW). Joint properties were evaluated through microstructural analysis and mechanical testing (tensile, impact, and microhardness). The thermo-mechanical behaviour of the CDFW process was simulated by the finite element method, while a computed continuous cooling transformation diagram was used to predict phase transformation, microstructures, and hardness variations. By reducing the spindle speed to 1000 r/min, the peak temperature in the weld centre zone (WCZ) remained below Ac1. Microstructures in WCZ exhibited a high density of geometrically necessary dislocations. The joints demonstrated comparable tensile strength, impact toughness, and microhardness to BM, with underlying mechanisms elucidated. This study showcases CDFW's potential in achieving rail steel joints with quasi-equal strength and toughness to the BM.