Q345E Thin Plate Small Deformation MAG Welding Process

Q345E steel has good mechanical properties,high strength,excellent plasticity and a certain degree of low temperature mechanical properties,with good weldability.In the welding production of high strength steel,the fusion welding with special properties is favored by many enterprises.Welding deformation is closely related to material,welding process and welding method.The welding deformation of thin plate is formed by the interaction of many factors and has diversity,which makes the welding deformation control technology has complexity and mutual restraint.The small deformation MAG welding process can prolong the service life and shorten the manufacturing cycle in thin plate welding production.In this paper,the low deformation welding process test of Q345 E low alloy and high strength steel with plate thickness of 3mm was carried out by the method of root welding and arc cold welding.The high frequency pulse and short circuit droplet transition form of the root welding mode not only ensures the penetration,but also reduces the temperature difference between front and back of the joint,thus reducing the welding deformation.The lower welding heat input in arc cold welding mode is beneficial to control welding deformation.By observing and analyzing the macroscopic morphology and microstructure of the welded joint,testing the tensile and bending mechanical properties of the welded joint,and measuring the Vickers hardness of the welded joint,the small deformation welding process was evaluated.By studying the variation law of welding thermal cycle,welding residual stress and welding deformation as well as the relationship among them,and using the finite element analysis software Abaqus to conduct numerical simulation of welding temperature field,stress field and welding deformation,the mechanism of welding deformation of thin plate is analyzed.The results are as follows:(1)The weld shape of the "0" gap condition of the root welding and the arc cold welding of the 1mm gap condition is good,without cracks,pores,slag and other welding defects.The tensile,bending and hardness tests of the welded joints meet the relevant standards.Therefore,when the group gap is "0",root welding(RW)process package can be selected;when the group gap is 1mm,Arc cold welding(CA)process package can be selected.(2)Fusion defects appear in the welding joints under the condition of 1mm gap in the root welding,tensile samples break on the weld fusion line,and bending samples crack obviously in the process of backbending experiment.This is due to the "high frequency compression effect" resulting in concentrated energy density and then supercooling during the cooling process.(3)The microstructure of each area of the welding joint under the three working conditions is basically the same.The boundary between the weld zone and the heat-affected zone gradually becomes obvious with the decrease of the heat input,and the grain size in the coarse grain zone gradually grows with the increase of the heat input.(4)The numerical simulation of welding temperature field,stress field and welding deformation is basically consistent with the measured results.The mechanism of thin plate welding deformation can be summarized as follows: when the front and back of the test plate are heated differently,the front and back of the test plate contract differently during cooling,resulting in angular deformation.After the angular deformation,under the action of longitudinal shrinkage stress,the corresponding deformation characteristics of "saddle shape" and "anti-saddle shape" are produced.After the deformation characteristics are determined,the deformation can be reduced by reducing the heat input and the thermal difference between front and back sides.