The Research On Residual Stress Of The S355Steel By MAG And Laser-MAG Hybrid Welding

The S355steel is a kind of low alloy high strength structural steel, which iswidely used in buildings, bridges, pressure vessels as well as rail vehicles.At present,with the rapid development of high-speed rail technology, the S355steel is widelyused in the manufacture of bogie frame. The welding process of the S355steelmainly uses MAG welding. With the development of welding technology,Laser-MAG hybrid welding technology becomes mature gradually. The Laser-MAGhybrid welding with large penetration, well clearance adaptable, small weldingdeformation and fast welding speed, has a broad application prospect in the field ofstructural steel welding.Due to the uneven heat input in the process of welding, welding residual stress isproduced in the weldment, and the values as well as the distributions of weldingresidual stress can lead to brittle fracture,fatigue damage,high temperature creepcracking,stress corrosion cracking and other kinds of damages. Therefore, analyzingand grasping the welding residual stress distribution of the S355steel is verynecessary to improve welding process and ensure the safety of the welding structure.In this paper,we make the standard butt sample by MAG and Laser-MAG hybridwelding; We simulate the welding temperature field and stress field of the MAGwelding by MARC software; We use the blind hole method to test the weldingresidual stress by MAG and Laser-MAG hybrid welding,respectively,and we alsoanalyze the distribution and the characteristic of the welding residual stress; The paperdiscusses the the basic mechanism which influences the residual stress distribution；What’s more, we predict the residual stress of the MAG welding of S355steel withdifferent welding sequence and groove forms.The results show that: there are some similarities of the residual stressdistributions between the MAG and Laser-MAG hybrid weldment. The maximummain stress appears around the center of the weld, and the farther away from theweld, the stress value are smaller. Along the weld direction, The farther away from the weld center, the tensile stress value decreases, and reduced to zero on both sides;Perpendicular to the direction, the longitudinal stress decreases to negative from theweld bead to both sides, that is, from the tensile stress area dramatically transition tothe compressive stress area.However,the specific distributions of the MAG andLaser-MAG hybrid welding have their own features.MAG welding use asymmetric X groove,and the line energy as well as thetemperature field distribution are different on both sides of the groove. On the smallgroove side,the width of the heat effect zone is small,and the maximum longitudinalstress are498.057MPa and504.62MPa when simulating and experimenting,respectively; On the big groove side,they are336.284MPa and405.58MPa,respectively. In contrast, the maximum longitudinal and the proportion of high tensilestress on the small groove side is higher than those on the big groove.The results ofthe measurement are basically in agreement with the simulation.Compared with the MAG welding, the heat source are apparently different oneither side of the Laser-MAG hybrid welding. On the Laser side,the line energy isbig,and the width of the heat effect zone is small, what’s more,the experimentingmaximum longitudinal stress are539.97MPa; On the MAG side,the stress are444.92MPa. In contrast,the maximum longitudinal and the proportion of high tensilestress on the Laser side is higher than those on the MAG side.The values and distributions of welding residual stress can make differencewhen changing the welding process,such as the welding sequence and the gro-ove forms of the MAG welding of S355steel. In consequence,using the simula-tion to predict the welding stress and deformation of the specimen is reasonab-le and efficient in production practice.