Effects of Phase Transformation on Distortion and Residual Stress Generated by Laser Beam Welding on High-Strength Steel

In order to elucidate the effects of phase transformation on distortion and residual stress generated by laser beam welding (LBW) on high-strength steel (HT780), a one-pass bead-on-plate welding experiment was carried out. Then, the experiment was simulated by the thermal elastic-plastic analysis. Because the mechanical properties in the phase transformation range could not be specified, they were idealized while considering the transformation expansion and the transformation superplasticity in the simulation of the experiment. The validity of the treatment of the mechanical properties in the phase transformation range was verified. It was elucidated that welding distortion and residual stress were largely affected by the phase transformation in the cooling process, although the bead width of LBW was extremely narrow, Angular distortion and tensile residual stress in the weld metal were largely released by the phase transformation.