The Welding And The Welding Joint Residual Stress By FEM Analysis For DH40 High-strength Steel With Heavy Plate

With high strength, low-temperature flexibility, corrosion resistance and anti-fatigue properties, DH40 steel is mainly applied to construction of large ships and offshore oil drilling platforms. Because of the nonuniform thermoplastic deformation and phase transformation by welding process, there are residual stresses in the joint which result in deformation, early cracking and brittle fracture. Therefore, weldability study on large thick DH40 steel is of importance to improve the operational reliability of the ship structure.In this paper, we consider DH40 high-strength steel (t=60mm) as the research object, and use multi-pass welding technology. In the different welding process parameters of welding joints, the microstructure of the M-A and the area percentage of M-A island which by FCAW, SAW welding methods are confirmed with the optical microscope and SEM. To analyze the inherent relation between the metallurgical microstructure and mechanical properties of weld joint, impact ductility and micro-hardness are tested in joint and HAZ. The results of the study indicate that: a certain number of big lump of hard and brittle M-A organization produce the stress concentration. Under the high tensile residual stress, impact toughness values of 5mm outside fusion line are decreased obviously.Additionally, based on ANSYS software, the finite element model (FEM) of DH40 high-strength steel plate X-shaped groove weld which thickness is 60mm is established by APDL. The welding residual stress distribution in thick plate is obtained by the temperature field and stress field analysis.The results show that: For the multi-layer multi-pass welding, the longitudinal residual stress in the joint and heat affected zone are the tensile stress, which the maximum value is 390MPa. After the peak, the longitudinal residual stress remains unchanged within a certain range. Oppositely, the longitudinal residual stress away from the joint is the compressive stress, and the maximum value is 296MPa. The transverse residual stress which along the welding line is usually the compressive stress, and in the middle of the joint, the maximum value is from 0MPa to 35MPa; at both ends of weldments, the maximum value is from 130MPa to 200MPa. The distribution curve tends to the parabolic distribution, the stress transits compressive stress gradually with the X-axis direction. In thickness direction, the stress are mainly the longitudinal and transverse residual stress, which inner weldments are less than surfaces, and then the longitudinal and transverse residual stresses on the upper surface are less than the lower surface. The through-thickness residual stress often fluctuates near zero along the thickness along the thickness direction.