Numerical Simulation Of Welding Temperature Field And Residual Stress Of Q345/316L Dissimilar Steel

The welding structures of dissimilar metal is widely used in petrochemical,power plant,pressure vessel,shipbuilding and so on,because of its excellent comprehensive performance,has the attention of the people.During the welding process,it will inevitably produce welding residual stress and deformation due to the local concentration and non-uniform heat input,thereby affecting the static load strength,accuracy,dimensional stability and stress corrosion cracking of welding structures and reducing welding bearing capacity and service life of the structure.At present,the studying on welding residual stress and deformation is less at home and abroad because of the limitation of experimental conditions and method,especially the study of dissimilar metal welded joint residual stress and deformation has not been formed a relatively perfect system.Therefore,carrying out temperature field,residual stress and deformation research of dissimilar steels welding by numerical simulation analysis helps to make up the shortage of experimental research,to provide the theoretical basis for dissimilar steels welding,which has very important significance.In this thesis,the numerical simulation and experiments have been used to analyze welding temperature field,stress field and deformation of 8 mm middle thick plate Q345/316L dissimilar steel welding by SYSWELD welding simulation software.The result show that Q345/316L dissimilar steel welding temperature field is asymmetrical distribution about weld center line,the high temperature range in the Q345 side are significantly wilder than in the 316L side,and there may be a certain degree of carbon migration near the fusion line in the Q345 side.The welding stress field is similar to ellipse shape and the asymmetrical distribution,give priority to with longitudinal residual stress of the workpiece residual stress,and the residual stress peak focus on the junction of Q345-weld.In the central cross section,the residual stress of welded joint distribution is relatively complex,large residual stress gradients existing near the fusion line in the Q345 side,and the distribution range of high tensile residual stress in the 316L side are obviously wider than in Q345 side.Simultaneously,both the numerical simulation and experiment results indicate that Q345/316L dissimilar steel joints produced obviously transverse shrinkage and angular distortion after welding.In addition,the measured results of welding thermal cycle curve,residual stress and deformation were in good agreement with the simulation results,which verified the effectiveness and reliability of the numerical computation method.The simulation results of the dissimilar steel welding structure parameters show that groove type have a certain effect on the welding residual stress,but the effect of welding deformation is more obvious.When viewed from the aspect of welding residual stress and deformation reduction,the K groove welded joints of opening toward the Q345 side is the best.Meanwhile,with increasing groove angle of V type,the residual stress distribution range and the longitudinal and transverse residual stress value of base materials near HAZ is growing,the transverse shrinkage and angular distortion of welded joint is also significantly increased,but a big groove angle can reduce the value of the residual stress in weld and fusion line.The layer number of dissimilar steel welding has little influence on residual stress.As the welding layer number increases,the residual stress in base materials and HAZ is decreased,the residual stress in weld has no obvious change,but the welding deformation of workpiece has increased rapidly.The simulation results of welding parameters show that the welding heat input has significant effect on residual stress and deformation of Q345/316L dissimilar steel welded joints.By increasing the heat input,the value and distribution range of residual stress and the transverse shrinkage and angular distortion of welded joint increased significantly,but on obvious changes are observed in weld.Moreover,the interlayer temperature has minor effect on the residual stress and welding deformation of dissimilar steel,but it has a great influence on the cooling rate of welded joint and the residence time in sensitization temperature zone.With the increase of interlayer temperature,it is easier to precipitate carbides and a phase,which can reduce the corrosion resistance of dissimilar steel welded joints.