Study On Laser-arc Hybrid Welding Process And Joint Performance Of Marine High Strength Steel

As a new welding method,laser-arc hybrid welding has the advantages of fast welding speed and strong bridging ability,which solves the problems of large thermal deformation and low welding efficiency of traditional welding method in marine high-strength steel,and has a promising future.However,the research on laser arc hybrid welding technology of 440 MPa marine high strength steel is less,so this paper takes 6 mm thick 440 MPa marine high strength steel as the research object to carry out I-groove laser arc hybrid welding butt test.The structure and mechanical properties of the welded joints were studied by optimizing the welding process,so as to provide the basic technical basis for the engineering application of laser-arc hybrid welding of 440 MPa marine high strength steel.Research on the influence of composite welding process parameters on weld forming quality shows that: The main reason for the bottom hump is that the laser hole fails to penetrate the workpiece continuously due to insufficient heat input in the welding process.Increasing laser power or decreasing welding speed can reduce the tendency of hump generation.For welding process of 6mm high-strength steel plate,the relationship between welding speed and laser power without bottom hump was determined by fitting test data.The fitting curve is in good agreement with the measured value and can be used as the basis for selecting the process parameters to control the hump defect at the bottom.The research on the influence of welding process on the weld shape of composite welding shows that: With the increase 0f welding speed,weld penetration depth and weld width decrease and Ha/Hl increase;With the increase of laser power,melting width increases and Ha/Hl decreases.Therefore,the fusion width and depth of composite zone are increased with the increase of arc heat input.Increase the laser heat input,melting width,melting depth of laser zone increase.According to the test results,the optimal process range of 6mm highstrength steel was determined: welding speed 1.2m/min-1.6m /min,laser power 5.0kw-5.5kw,wire feeding speed 4 m/min-6 m/min,which can realize single side welding double side forming,and the weld section is uniform and symmetrical.The microstructure study of hybrid weld joint shows that: The microstructure of hybrid weld metal is fine and uniform,and the grain size is between MAG welding and laser welding,The microstructure mainly composed of acicular ferrite,lath bainite and a small amount of proeutectoid ferrite.With the increase of welding speed and the decrease of laser power and wire feeding speed,the grain size of hybrid welding metal become smaller.The quantity of the proeutectoid ferrite and side plate ferrite decreased gradually,the acicular ferrite and lath bainite increase.The coarse-grained area of composite welding consists of lath martensite and lath bainite.With the increase of welding speed,the decrease of laser power and wire feeding speed grain size in the coarse-grained area decreases gradually,and the influence of welding speed is more significant.The mechanical properties of the hybrid weld joint show that: Increasing the welding speed,reducing the laser power and wire feeding speed can increase the hardness of the weld,and the welding speed has a significant impact on the hardness of the weld.Under different welding processes,the fracture position of hybrid weld joint in tensile test is located in base metal,and there is no crack in bending test.With the increase of welding speed,the laser power and wire feeding speed decrease,and the weld toughness increases gradually.The impact energy of weld decreases with the increase of arc heat input or laser heat input,but the effect of laser heat input on weld toughness is more significant than that of arc heat input.Hybrid welding parameters have little effect on the toughness of HAZ,and the width of coarse-grained zone in HAZ has good toughness,for the narrow width of HAZ.