Evaluation of Residual Stress and Its Influence on Fracture Performance of Q690 Thick Plate Butt Welded Joint

Objectives As main component of offshore, welded structure with thick plate of high tensile strength steel has complicated residual stress which is difficult to accurately and comprehensively evaluate, and it will directly influence the fracture performance of welded joint and maintenance cost of offshore. Methods Taking Q690 high tensile strength steel with 75mm thickness as research object, butt welding processing for multi pass was made and its corresponding welding experiment was also carried out, and longitudinal residual stress on middle cross section was measured with contour method after cooling down. Results Based on effective thermal elastic plastic FE computation, behaviors such as thermal cycle, evolution of microstructure during multi pass welding of thick plate were represented, and predicted shape of welded pool as well as content of metallographic phase has a good agreement with measured data. With considering welding solid phase transformation and initial stress due to rolling, welding mechanical analysis obtained longitudinal residual stress well compared to measured results and transverse residual stress was also obtained. Combining experiment of axial tension and GTN damage model together, parameters of GTN for Q690 high tensile strength steel was presented, which was then employed to examine fracture performance as well as curve of stress-strain for base metal and specimen of welded joint. Moreover, fracture performance of examined welded joint of thick plate was also investigated with considering welding micro defect and transverse residual stress, while its mechanical mechanism due to welding residual stress was clarified. Conclusions Research and its result can be experience to evaluate residual stress and fracture performance of welded joints with high tensile strength steel and thick plate.