Analysis of welding residual stress in multi-pass hybrid laser-MIG welded X80 pipeline steel

Combined experimental and numerical investigation of temperature field and residual stress field of X80 pipeline steel multi-pass hybrid laser-MIG welding were performed. Influence of laser power on microstructures, temperature distribution and residual stress distribution in the hybrid welded joints were analyzed. The results show that rising maximum temperature of the molten pool and decreasing post-welding cooling rate were obtained with increasing laser power. More acicular ferrite and granular bainite, less lath bainite formed in the coarse grained heat affected zone. Overall residual stress level in the X80 pipeline steel hybrid welded joints were high with peak tensile stress occurred in the weld metal for longitudinal stress, transverse stress and through-thickness stress. In the laser power range from 2.0 to 3.5 kW, peak stress of Von Mises equivalent stress, longitudinal stress, transverse stress and through-thickness stress all decreased with increasing laser power. However, peak stress of the stresses increased with laser power increasing from 3.5 kW to 4.0 kW.