Study On The Evolution And Regulation Mechanism Of Welding Residual Stress In The Welded Joint Using Low Temperature Transformation Welding Wire

Welding residual stress is an important factor affecting the reliability and safety of mechanical equipment in large-scale,high parametric,complex and harsh conditions during long-term service.It is also the main cause of fatigue fracture,brittle failure and various welding cracks.Based on the innovation of welding residual stress and deformation control theory,a submerged arc welding wire which can be relieved of stress after welding was developed and applied to EH40 high strength marine steel plate welding.In view of the limitations of traditional numerical calculation models in predicting the complex thermos-physical/metallurgical physical behavior of welded joints under multi-factor coupling conditions,a non-linear strong coupling finite element calculation model describing the thermo-mechanical-metallurgical behavior of low phase transition alloys under strong constraints,unsteady states and complex thermal cycles was established based on the finite element analysis software ABAQUS/Standard,which can be accurately predicted.The formation and evolution trend of welding residual stress/structure of low temperature phase change alloys were measured.The main conclusions of this paper are as follows:(1)A submerged arc welding wire for high strength steel without post-weld stress-relief treatment was developed.The wire has the characteristics of self-adjusting the residual stress level of welded joints through low temperature martensitic transformation.During the cooling stage,the volume expansion effect caused by low temperature martensitic transformation at the weld seam can offset the accumulation of residual tensile stress during the cooling shrinkage process,reduce the residual tensile stress and form a stable compressive stress zone in the weld zone.(2)The multi-field evolution law of heat input-phase transformation-stress deformation of welded joints was studied by numerical analysis method,and the evolution of residual stress under different phase transformation temperatures and inter-pass temperatures was analyzed.The results show that the phase transformation temperature of low phase transformation spot welding material has significant influence on the level and distribution of residual stress.The lower the phase transformation temperature is,the residual stress level at the weld center is.The lower the welding temperature is,the higher the starting temperature of martensitic transformation is,and the more martensitic transformation is avoided during welding,the more uniform the distribution of residual compressive stress is and the higher residual tensile stress is avoided at the bottom of the weld.The numerical simulation of residual stress is consistent with the results of neutron diffraction measurement,which shows that the solid phase transformation is considered.The numerical simulation method can effectively and reliably predict the welding residual stress distribution of low phase transformation point alloys.(3)The effect of transformation plasticity on the evolution of welding residual stress is clarified by numerical analysis.The results show that the abnormal plastic deformation of low transformation point alloys induced by the phase transformation plasticity effect caused by the mismatch of two phases(martensite phase and austenite phase)during the rapid cooling stage of welding can weaken the inhomogeneity of micro plastic strain of each phase and inhibit the weld metal.Stress accumulation results in the relaxation release of longitudinal and transverse residual stresses in the weld zone.Moreover,the larger the value of transformation plasticity parameter K,the more significant the residual stress relaxation effect.