Comparison of welding temperature fields, residual stress distributions and deformations of Gas Tungsten Arc (GTA) and ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA) welded DP780 steel joints

Abstract

Considering the excellent anti-corrosion property in chlorinated mediums and comprehensive mechanical properties of dual phase steel, this kind of steel plate will be widely used in the future. However, when ordinary welding methods are used to weld these steel sheets, large deformation usually occurs during local heating due to the lower stiffness of sheet joints. Based on a thermo-elastic-plastic Finite Element Analysis (FEA) method, considering both material non-linearity and geometric non-linearity, the temperature field and deformation of DP780 steel thin-plate welded joints using Gas Tungsten Arc (GTA) welding and Ultrasonic-wave-assisted Gas Tungsten Pulsed Arc (U-GTPA) welding is simulated. Through the combination of experiment and numerical simulation, the difference in the simulation process for the weld deformation of sheet joints caused by GTA welding with and without acoustic-controlled arc is clarified. In particular, the effects of acoustic-controlled arc and external confining positions on the weld deformation, and residual stress distribution of duplex phase steel joints welded by two welding methods are compared. The research results indicate that the welding heat source of U-GTPA has a smaller acting range on the workpiece and a higher peak temperature (up about 200 °C) than that of GTA. Replacing the traditional GTA with U-GTPA can reduce weld deformation, the maximum buckling deformation of welded sheet is only 4.2 mm and the rate of deformation is reduced by 60%. The numerical simulation confirmed that the high longitudinal tensile stress ranges in U-GTPA-welded joints are narrower than that in GTA-welded joints, but the maximum longitudinal residual stress generated by U-GTPA welding is greater than that generated by GTA welding. Furthermore, the stress distribution in the fusion zone and its surroundings, as well as the out-of-plane deformation of the steel sheet can be further controlled by optimizing the confining positions. The selection of the appropriate restraint positions is also an important factor to the optimization of the U-GTPA welding process.