2010 Volume 28 Issue 3 Pages 281-287
In order to elucidate distortion and residual stress generated by welding of high strength steel (HT780) by laser beam, a series of experiments and analyses were carried out. The angular distortion generated by bead-on-plate welding was V-shape and its magnitude was about 2mm. The longitudinal bending distortion was extremely small. On the surface of plate, the residual stress component in welding direction was tensile and it was smaller than yield stress in the weld metal. The residual stress was almost zero outside the weld metal. The phase transformation range in cooling stage and the temperature dependency of mechanical properties were obtained. The mechanical properties in the phase transformation range in cooling stage could not be specified due to transformation expansion. Therefore, they were idealized by considering transformation expansion and transformation superplasticity. The validity of the idealized mechanical properties was verified by simulating the experiment by the thermal elastic-plastic analysis. It was elucidated that the welding out-of-plane distortion and tensile residual stress were largely controlled by phase transformation in cooling stage although the bead width of laser beam welding was extremely narrow.
