Reseach On Bainitie/Martensite Duplex-Phase Rail Steel Weldability Of Heavy Haul Railways

Heavy haul railways shoulder the heavy responsibility for long-distance transportation of bulk goods such as coal and ore.With the continuous growth of China’s freight volume,the requirements for rail are getting higher.Theoretical studies have shown that it’s difficult to increase the mechanical properties of traditional pearlite rails.Bainitic rail with higher strength and better wear resistance has good application prospects.However,the welding problem has become the key to restricting the popularization and application of bainitic rail steel.For welding the bainitic rail successfully and extending rail inservice tme to ensure the safe operation of the line.Using GPW-1200(75)gas pressure welding machine with completely independent intellectual property rights in our country and referring to 75kg/m U78 CrV pearlitic rail gas pressure welding process to complete the experiments of welding bainitic-bainitic rail and bainitic-U75 V rail.Drop hammer,metallographic and hardness tests manifest that the fracture characteristics of welded joints are less,the segregation of zonal structure is serious,the hardness variation trend is similar to the pearlite steel rail and the quality of welded joints are unsatisdactory.Using GPW-1200(60)gas pressure welding machine and referring to 60kg/m U78 CrV pearlitic rail gas pressure welding process to complete the experiments of welding bainitic-bainitic rail.Drop hammer,metallographic and hardness tests manifest that the fracture characteristics of welded joints are less,the segregation of zonal structure is serious,the hardness variation trend is similar to the pearlite steel rail and the quality of welded joints are unsatisdactory.with the same welding process,the characteristics of welded joints are not reproducible.Adding transition layer,adjusting the forging pressure and extrusion deformation mode to completed the gas welding experiments.The quality of the welded joints are not satisfactoryDesigned and manufactured the induction heating and pressure device which can simulate the heating and forging process of gas pressure welding.Using the device to completed the small samples welding experiments.Using the three point bending method to break the welded joints,researching the relationship between fracture characteristics and metallographic structure,and hardness distribution.The tests manifest that use the process of heating(electric current1190±10A,135s);heat preservation and forging((electric current1090±10A,30 s,forging length 5~8 mm,forging velocity: 0.2mm/s)to weld the small samples,the fracture characteristics of welded joints are good.Doing experiments with different forging velocity(0.2~6mm/s),The tests manifest that the lower forging velocity,the condition of interactive crystallization and dynamic recrystallization of weld metal better.Through the observation of the microscopic characteristics of weld,the fracture features show that level state also achieved the interactive crystallization,but the weld microscopic structures are different.The above research results provide a scientific basis for solid phase welding of bainitic rail.