Accurate evaluation on residual stress considering solid-state phase transformation and initial stress in thick weld

During the welding process of thick plates, it is difficult to evaluate the residual stress distribution in thick welds accurately because complicated residual stress is generated by multi-thermal cycles. In this study, a multi-pass butt joint was fabricated using Q690 high strength steel with the thickness of 75 mm, meanwhile experiments were carried out to characterize the microstructure and measure the through-thickness distribution of longitudinal residual stress in a butt-welded joint by the contour method. Then numerical methods were developed to predict the through-thickness distribution of residual stress in butt-welded joints. To evaluate residual stress accurately and efficiently, the effects of solid-state phase transformation (SSPT) and initial stress were taken into consideration, and the parallel computation technology and iterative substructure method were employed. The root-mean-square error (RMSE) was employed to evaluated the prediction accuracy of numerical methods between measurement and numerical results of residual stress. Through comparing the simulated results with experimental data, the validity of the developed numerical methods was verified. Numerical results indicate that the through-thickness distribution of residual stress in butt-welded joints is very complex and peak value of tensile stress can be found in the area adjacent to the heat-affected zone (HAZ). Moreover, the RMSE is significantly decreased from 307 to 8 when considering the effect of SSPT on residual stress in weld vicinity, and the RMSE is apparently decreased from 137 to 11 when considering the effect of initial stress on residual stress in base metal.