| It were studied synthetically that the flash butt welding parameters, welding thermal process and microstructure of axisymmetric 45 steel in this paper,.The optimized flash butt welding parameters of axisymmetric 45 steel of 16mm in diameter and 100mm in length were determined utilizing the orthogonal test. Single level orthogonality form L9 (34) was selected to design the experiment scheme and it chose tensile strength of welding joint as the index for quantitative, initial overhang, flashing current density, flashing time, secondary floating voltage as the experiment factors, each of them has three bit levels. The interactions among the factors were ignored. The optimized combination of parameters were initial overhang 15mm, output current percentage 80%, flashing time 6s, secondary floating voltage 6.23V. The secondary floating voltage is the important parameter and it influences the performance of welding joint significantly. The tensile strength of welding joint with this optimized combination of parameters is 702MPa, higher than that of the matrix.The three point bending test indicated that the plasticity of welding joint was worse than that of the matrix. The analysis of microstructure is as follows: the grain size is finer gradually from the weld to the overheated zone to the phase change zone with the peak temperature fall along with the distance going up away from the weld, the austenitic grain size of the overheated zone is large and Widmanstaten structure is formed, which is the cause of the toughness fell. The microstructure transformation and the grain size distribution were analyzed in different zones of welding HAZ. And the interactions of the temperature, microstructure and performance were discussed.The flash butt welding temperature distributions of axisymmetric 45 steel based on the optimized parameters were measured by the temperature test system. The relation between theaxial temperature T(x) and the distance x was described as lnT(x) = K(a + bx + cx2 + dx3), theradial temperature of the same cross-section rose from the exterior to the interior and assumed parabola regularity. The weld thermal cycle curve of flash butt welding HAZ was divided into calefaction and refrigeration phases by peak temperature Tp, and was fitted.A simplified thermoelectric coupling 2-D axial symmetry model of flash butt welding was founded based on finite element analysis. With the fact of flash butt welding and the characteristic of material properties varied with temperature, the influences of the contact resistance and the phase change latent heat on heat generation process were considered in this model. The temperature distribution of each time and the weld thermal cycle of each position in the heating process were obtained in the simulation. The comparison of the simulated... |
