A study on the effect of gap width on residual stresses of laser-welded dissimilar joints

Laser-welded parts experience high local temperatures and severe heating-cooling cycles which lead to large local residual stresses. These stresses introduce unacceptable degradation of the mechanical properties of a weldment. Thermo-elasto plastic analyses with 3-D FE models, as well as experimental investigations were performed in order to pre lilt temperature distribution and residual stresses of ND-YAG laser-welded joints with various gap widths between the dissimilar steel types of austenitic and precipitation-hardening stainless steel. The specimens have the shape of a pocket to optimize the weight of the structure, which consists of a thin skin (AISI304) and a thick skeleton (AISI630). The residual stresses at the surface of the weldments were measured using the instrumented indentation method. The residual stresses and rnelt-pool zone (MPZ) profiles show good agreement between the theoretical and experimental results. Considering the residual stresses, the allowable gap width range of the laser-welded joints for the pocket-shaped specimen was calculated. For a welding joint with gap widths, the longitudinal residual stress values at the yield stress level were observed. Melt-pool zone profiles described by the underfill and penetration depth also depend upon the gap size.