Numerical Study on Welding Residual Stress and Microstructure in Gas Metal Arc Welding Square Tube–Plate Y-Shaped Joints

Welding residual stresses significantly influence the mechanical behavior of hollow section joints, especially in the pivotal connection zones of steel structures employed in construction. The research object of this study is the Q355 steel square tube–plate Y-joint welded using Gas Metal Arc Welding (GMAW) with CO2 Shielding. The thermodynamic sequence coupling method was employed to simulate the temperature field, microstructure distribution, and welding residual stresses in square tube–plate Y-joints. Based on the monitored temperature field data and the cross-sectional dimensions of the weld pool, this study calibrated the finite element model. Subsequently, the calibrated finite element model was employed to analyze the influence of microstructural phase transformations and welding sequences on the welding residual stresses in square tube–plate Y-joints. The research findings indicate that the peak transverse welding residual stresses in the branch pipes of the four joint zones were lower when considering the phase transformation effect than when not accounting for it in the calculations. There was no significant difference in the transverse and longitudinal welding residual stresses on the surface of branch pipes under the three welding sequences. However, there were certain differences in the microstructural content of the weld zones under the three welding sequences, with the martensite content in the third welding sequence being significantly lower than that in the other two sequences.