Effect of mechanical vibration on microstructure and impact properties of gas metal arc welding Q450NQR1 welded joints

Abstract

This article was focused on studying the influence of microstructure and impact performance of Q450NQR1 weathering steel welded joints using low-frequency mechanical vibrations during the welding process (GMAW). The analysis of the molten pool cooling and solidification process in vibration welding is conducted using a one-dimensional Stefan problem and the wave equation coupled model The computational results show that the molten pool cooling time decreases and the stress on the dendrites increases during the crystallization process as vibration frequency increase. Mechanical vibrations with a fixed amplitude of 0.1 mm and frequencies of 0, 20, 40, and 60 Hz were applied to the welding molten pool under the same welding parameters. The microstructure of the weld joints was examined using metallurgical microscope. Charpy impact test was used to measure the impact properties. The results show that the increase in weld zone width is accompanied by a reduction in the heat-affected zone width after the application of mechanical vibrations. The primary proeutectoid ferrite dendrites undergo fragmentation. The acicular ferrite content has increased and structural refinement. The impact energy in the weld zone increases with the increase in vibration frequency. The welded joints exhibit enhanced toughness, with an increased proportion of the fibrous region (F) and the shear lip region (S) at the fracture surface. The distance between the crack instability position and the root of the notch increases.