Study On Fatigue Properties Of T-shaped Double-sided Laser Welded Joints Of Weathering Steel

In recent years,our country's rail passenger cars have developed by leaps and bounds,and people have higher requirements for the safety and reliability of rail passenger cars.Weathering steel has the characteristics of low price,good welding performance and easy maintenance,and is currently an important material for rail passenger car bodies.T-welded joints are widely used in rail passenger car bodies.However,as a welded structure,there is a big problem of welding fatigue,and the welding fatigue performance directly affects the reliability of the rail car body.Therefore,it is necessary to study the fatigue properties of welded joints to ensure the reliability of rail passenger car bodies.In this paper,the fatigue properties of T-shaped double-sided joints of weathering steel are studied and compared with those of T-shaped single-sided joint of weathering steel.The specific research contents are as follows:The microstructure and microhardness of the T-joint were analyzed through experiments,and the results showed that the T-shaped double-sided joints of weathering steel can completely cover the welding area.The metallographic structure at the base metal of T-shaped double-sided joint is mainly ferrite,the metallographic structure at the heat affected zone is finer ferrite and pearlite,the metallographic structure at the weld is distributed in columnar crystals,and there are fine ferrite and pearlite in the columnar crystals.The hardness of the weld is the largest,followed by the heat-affected zone,and the hardness of the base metal is the lowest.The tensile properties of the T-joint are analyzed through the test,and the results show that the maximum force of T-shaped double-sided joint is 19.408 k N.Plastic deformation and fracture occur at the base metal.The tensile strength of weld is higher than that of base metal,which belongs to "high strength matching".For static load tension,the weak position of T-shaped double-sided joint is in the base metal rather than the weld,which can meet the tensile requirements of rail car body.The finite element model of T-joint was established by finite element analysis software,and its temperature field,stress field and fatigue performance under a given cyclic load were analyzed.The results show that the weld pool temperature of T-shaped double-sided joint is higher than that of T-shaped single-sided joint,which is due to the preheating effect of the first side weld on the second side weld;The welding residual stress of T-shaped double-sided joint is less than that of T-shaped single-sided joint.This is because the second weld is equivalent to the tempering of the first weld,which can eliminate the residual stress to a certain extent.Under the same cyclic load,the fatigue life of T-shaped double-sided joint is higher than that of T-shaped single-sided joint.The failure position of T-shaped double-sided joint is at the weld toe,and the failure position of T-shaped single-sided joint is at the weld root.The fatigue properties of T-type joints are studied through experiments,and the results show that the fatigue limit of T-shaped double-sided joint is 4.811 k N,reaching24.56% of static load tension.The fracture is located at the weld toe.The fatigue limit of T-shaped double-sided joint is 1.45 times that of T-shaped single-sided joint.The threshold value of crack growth gate of T-shaped double-sided joint is greater than that of T-shaped single-sided joint,which is less prone to crack initiation.Under the same stress intensity factor,the crack growth rate of T-shaped double-sided joint is less than that of T-shaped single-sided joint,and the range of crack growth stage of T-shaped double-sided joint is larger.The fracture modes of the two T-type joints are the "throughseam and through-plate" fracture mode,the difference is that the T-type double-sided cracks are initiated at the weld toe,while the T-type single-sided cracks are initiated at the weld root.The stress concentration of the type single-sided joint is more serious.Compared with T-shaped single-sided joint,T-shaped double-sided joint has better fatigue performance.