Study On Microstructure And Mechanical Properties Of 45 Steel Diffusion Welded Joint

The fusion welding was the most frequently-used welding technology in the industry,fusion welded joint could realize equal intensity with the base metal in accordance with the principle of equal match,however,the difference among different zones in microstructure and mechanical properties was large due to its asymmetric heat input.To realize the equal match between the joint and the base metal in composition,microstructure and mechanical properties was the goal that welding researchers were pursuing.Diffusion bonding of 45 steel and the composition,microstructure and mechanical properties of the joints were studied in this paper to test and verify whether the diffusion joint could the equal match with the base metal.Line scanning and area scanning of composition were analyzed by scanning electron microscope,the distribution of elements adjacent to combining zone was uniformMicrostructure of the joints was observed by metallographic microscope,the welding interface could not be observed in combining zone;Microstructure of the diffusion joint was uniform and identical with the base metal;the size of grain in the combining zone was equal to the base metal.Basic mechanical properties test result showed that tensile specimens in both welding and annealing state were broken in the base metal,which proved the intensity of the welding joint was not lower than the base metal;The tensile strength of the welding joint was 609.7MPa,the yield strength of the welding joint was 290.7MPa,the ductility of the welding joint was 14.3%;The impact toughness of the base metal was 37 J,the impact toughness of the welding joint was 36.5 J,which was nearly equal to the base metal;After quenching and annealing the tensile strength of the joint was 814.8MPa,the yield strength of the joint was 677.7MPa,the ductility of the joint was 10.3%,the impact toughness of the joint and the base metal were 43J and 44J;There were a large amount of dimples in the tensile fracture,the tensile fracture was tough fracture.The result of fatigue test showed that almost fatigue samples in both welding and annealing state were broken in the base metal,which proved the fatigue strength of the joint was not lower than the base metal;The fatigue limit of the joints in the welding state was 208.1MPa,the fatigue of the joints in the quenching and tempering state was 363.7MPa;The fatigtue strength of the welding joint and the joint after heating were 223.5MPa and 378.8MPa through matching the curves of S-N for the livability of 50%by the means of the least square method.Analysis of fatigue fracture showed that fatigue fracture were composed of fatigue initiation,crack propagation zone and final rupture region;the fatigue crack initiates from the surface of fatigue sample,fatigue crack propagation were composed of fatigue striations and tearing edges,the second crack could be observed in local area;the fracture morphology of transient fault zone was tough fracture.The diffusion welded joint could realize the equal match with the base metal in composition,micro structure and mechanical properties.