Research On The Weldability Of Q690 High Strength Steel And Numerical Simulation Of Residual Stress

Nowadays,high strength low alloy steel(HSLA)has been widely used in shipbuilding,pipeline transmission,heavy machinery and ocean platform for its excellent property and good weldability.With the rapid development of these mentioned industrial fields,welding technology has become irreplaceable technology in large steel structure connection.However,the welding joint is usually the vulnerable point of the whole welding structure.Through the analysis of fracture failure accidents of welding structure in the last century,insufficient understanding of the material weldability and improper selection of welding procedure,causing cold cracking in the weld heat affected zone(HAZ),are the main reasons of the fracture accident.Therefore,y-groove cracking test around HSLA Q690 was studied.Through the thermal elastic-plastic finite element method to the simulation of welding experiment,the influence of welding process(welding heat input and preheating temperature)on residual stress distribution after welding is systematically analyzed from the combination of finite element simulation and welding cold crack test,and the process of cold crack formation is explained.The main research contents are as follows:(1)Using submerged arc welding technology,three different welding heat input(0.92kJ/mm,1.38kJ/mm,and 2.05kJ/mm)were used as research variables in y-groove cracking test.The test results showed that only when welding heat input was 0.92kJ/mm and 1.38kJ/mm,macroscopic cold cracks appeared in HAZ;Using submerged arc welding technology,welding heat input is controlled within 1.38?1.54kJ/mm,which can meet the needs of general engineering;According to the observation of the welding cold cracking morphology,the crack initiation always occurs in the coarse grain heat affected zone,gradually expanding to the center.(2)Thermal elastoplastic finite element method was used to simulate the welding cold crack test.The welding temperature field was simulated by using the Goldak double ellipsoid heat source model,with regarding preheating temperature and welding heat input as variables.The macroscopic metallographic method was used to check the shape parameters of the heat source model to obtain the accurate welding temperature field distribution.The welding stress field is simulated based on the welding temperature field.The simulation results show that the welding residual stress is mainly concentrated in the welding root and HAZ of the arc-starting and arc-ending sections,and the welding residual stress of the straight Y groove side is higher than that of other side.With the increase of preheating temperature,the concentration degree of welding residual stress in the welding root and HAZ is increased obviously.Increasing the welding heat input can effectively reduce the residual stress concentration at the welding root.The influence of preheating temperature and welding heat input on transverse residual stress is greater than that on longitudinal residual stress.In addition,through the analysis of equivalent residual stress at the root of the weld,it can be seen that the residual tensile stress in the coarse grain heat affected zone is significantly higher than that in other zones,which is highly consistent with the test results(the crack initiation always occurs in the coarse grain heat affected zone).