The application of U20 Mn bainte/martensite duplex-phase rails with high strength and wear-resisting in heavy-duty lines is restricted by the poor quality of flash welding. Using the special device which assembled high-frequency induction on the hydraulic press to weld small U20 Mn rail samples,simulating heating and forging process of gas pressure welding. Doing plastic pressure welding experiment under the process of same heating input and forging length,different forging velocity. Metallurgical welding behavior of welding crystallization and fracture feature at welding interface were observed and researched. The results show that bainte/martensite duplex-phase rails can realize metallurgical welding under the condition of plastic heating,forging length（5～7 mm）,forging velocity is less than 6 mm/s. However,with the forging velocity increases,the grain size of the weld metal interaction crystallization becomes smaller,the difference between the grain size and the parent grain become greater,the degree of brittle fracture are greater.