A Study On Microstructure, Hardness And Torsional Fatigue Behaviors Of 16MnR Welding Joint

Many researches focus on the welded bogie, however, few achievements on fatigue behaviors of the welded bogie have been obtained. In this study, a series of experiments were carried out on the welded joint made by 16MnR steel which is representative for the welded bogie. The microstructures and hardness of different zones (welding line, heat affected zone (HAZ) and base metal) of the joint were measured by metalloscope and Vicker's indentation tester, respectively. Besides, the behaviors of the low-cycle fatigue in different zones of the welding joint were compared and the influences of the relevant microstructures on it were studied as well.The results indicated that columnar grain structure existed in the map pass of the joint, and the horizontal microstructures were similar but the sizes turned smaller; while pro-eutectoid ferrites, a small amount pearlites and several carbides equiaxedly distributed in filler passes, where the grains looked homogeneous and fine. The microstructures in relevant HAZ were composite, mainly acicular ferrites, fine pro-eutectoid ferrites and a few pearlites.The hardness of wielding line and base metal were similar. However, the hardness of HAZ were obviously higher than those of wielding line and base metal and presented a gradient distribution with the highest value near welding line. The shear modulus and stress amplitude in HAZ were significantly higher than those in the other two areas as well, making it easier to get fatigue.On the whole, there existed several relationships among inhomogeneities of microstructures, hardness and fatigue behaviors of 16MnR steel joint. The areas with better microstructures and homogeneous and fine grains, such as the second and third lines of wield, held relatively higher hardness and longer fatigue lives.