Microstructure and properties of radial friction welded joint of 37CrMnMo steel pipe

With self-developed radial friction welding machine,37CrMnMo steel pipe was welded at the optimized welding parameters by taking 45 steel as ring.Experimental results show that the ring has serious plastic deformation and there is a narrow HAZ in 37CrMnMo steel pipe body and the weld is oxidized.The mean shear strength of the weld can be up to 401 MPa,which is higher than that of 45 steel.The appearance of shear fracture is smooth and characterized by shear dimple,which indicates that the weld has high ductile and plastic properties.The microhardness is decreased from the bonding center to both sided of 45 steel ring and 37CrMnMo steel pipe.The analyses on microstructure of the joint show that there is a very good narrow metallurgical bonding zone between steel ring and steel pipe,but overheated zones appears in HAZ of 45 steel pipe and 20 steel ring.The HAZ in 45 steel side is ferrite,pearlite and bainite,and that in 37CrMnMo steel side is bainite and a few martensite.Compared with base metal,hardening microstructure appears in HAZs of 45 steel and 37CrMnMo steel because of high cooling rate,but the microstructure in the weld is finer than that of base metal under the thermo-mechanical coupling interaction.