Investigation On Welding Residual Stress Of TA2/Q345 Clad Plate Using Coverplate-lap With Complex Structure

Due to excellent corrosion resistance and high strength,the TA2/Q345 clad plate ha s wide potentials in the aerospace,petrochemical industry,marine engineering and other fields.However,large residual stress is easily generated around the welding seam during welding TA2/Q345 clad plate because of the large differences in the temperature field and their thermophysical properties.The residual stress promotes the initiation and propagation of cracks,thereby deteriorating the performance of the structure and reducing the service life.In this investigation,the evolution of temperature field and stress field along with the stress regulation during the welding process of TA2/Q345 clad plates were studied utilizing coverplate-lap with complex structure.The research can provide the therotical basis for the welding design and the improvement on the welding quality for heterogeneous materials.Based on the thermo-elastic-plastic finite element theory,the evolution of temperature field and stress field during welding TA2/Q345 clad plate utilizing coverplate-lap with complex structure was reconstructured by the numerical simulation method along with change of the material properties for the filling unit.During welding clad plate,the baseplate molten pool is in the form of oval shape,whereas the subplate and coverplate present spoon-like shapes if the welding reaches a quasi-steady state.The welding of clad plate not only obviously influences peak temperature,but also affects heat dissipation at and around the interface of the TA2/Q345 clad plate.The stress field was simulated by the calculated result of the temperature field as the initial load,and it is found that there is a small change for the stress in the middle of the welding seam.The longitudinal stress is in the tensile state,while the transverse stress alternately changes in the tension-compression state.However,due to the change of the temperature field,the stress has an extremely complicated change at the ends of the welding seam,and the amplitude is significantly changed as well.Meanwhile,for the baseplate and coverplate after welding,the stress at the joint exceeds the yield strength of the two kinds of materials,and the peak stress at the interface of the TA2/Q345 clad plate is larger than that at the welding seam after subplate is welded.To ensure the safe operation of the clad plate components during service,the influence of welding residual stress on the bearing capacity,interface bonding strength and corrosion resistance was investigated.The effect of welding process on the baseplate,subplate and coverplate on the clad plate was discussed separately.The results show that the increase of preheating temperature and decrease of interlayer cooling time can effectively reduce the baseplate welding residual stress;the decrease on the arc power and interpass cooling time,the increase on welding speed,and the synchronous welding sequence along with the same direction can reduce the residual stress at the interface and weld surface of the coverplate,and increase the yielding rate as well.Due to the limit of the stress regulation of the clad plate for the single factor under the constraint condition of the joint,the regulation investigation of multi-factors was made for the welding process of the three regions.It is found that the load-carrying capacity of the baseplate is improved effectively at the preheating temperature of150°C and cooling time of 100 s.When the subplate is used,the minimum welding residual stress can be obtained at the cooling time of 100 s,the welding power of 450 W,the welding speed of 3.2mm/s accompanying the synchronous welding sequence along the same direction.At this case,the peak stress is reduced up to 21.3%,and the effect of the welding process of the subplate on the residual stress of the interface can be ranked as S>t>P>v.When the coverplate is welded,the optimum process is the combination of synchronous welding along the same direction,200/1000 s,1000W and 1.2mm/s.The peak equivalent stress can be reduced by 31%,the stress at the weld surface has the mimimum effect on the corrosion resistance,and their effect can be ranked in the order of S>t>v>P.The TA2/Q345 clad plate utilizing coverplate-lap with complex structure was welded using the optimized parameters by simulation,the weld pool morphology was characterized by the thermal cycle curve and stereomicroscope,and the residual stress was measured using the blind-hole method.It is found that the measured values are in good accordance with the calculation results,and the the tensile and shear properties can meet the actual requirements of the optimization process.