The influence of phase transformations on residual stresses induced by the welding process - 3D and 2D numerical models

In this work, a numerical study of laser beam welding of steel was performed. In particular, phase transformation effects were considered, which consist mainly of volume change and transformation plasticity. Thanks to the possibilities of numerical modelling, additional analyses were performed (a) without taking into account phase transformations and (b) considering only the transformation plasticity phenomenon. The aim of this study was to examine the influence of phase transformation on the residual stress induced by the welding process, by comparing the results obtained with the described differences in the analyses. Finally, the residual stress field computed by the three-dimensional (3D) model was compared with the one computed by a two-dimensional (2D) model in order to estimate the grade of reliability of the more efficient 2D analyses, also in the presence of phase transformations. It was found that both volume changes due to phase transformations and transformation plasticity have a great influence on the residual stress induced by the welding process. 2D numerical models can be used with good accuracy instead of 3D models, if the in-plane stresses are of primary interest. All analyses in this investigation were performed with the finite element code SYSWELD®.