Research Of Laser-Induction Hybrid Welding Processing On S690QL Steel

High strength low alloy(HSLA)steel S690 QL is widely used in offshore platform,construction and other engineering fields.With the improvement of human society,science and technology,the requirement of welding structure quality becomes higher and higher,the main factors that determine the quality are the microstructure and performance of welding joints.Recent years,due to the laser hybrid welding technology can combine the merits of both laser and the other heat sources,achieve the effects of ‘1+1>2',the development of laser hybrid welding becomes rapidly.In this paper,HSLA steel S690 QL was chosen to conduct the research of LIHW processing,welding stability,weld geometry and microstructure formation,as well as performances.The relationship of welding processing-welding formation-performances were established and the laser-induction hybrid welding(LIHW)processing was evaluated comprehensively.As two methods of LIHW,the welding heat absorption and utilization efficiency,weld depth and width of induction pre-heating LIHW are deeper than induction post-heating LIHW.Based on the electron backscatter diffraction(EBSD)technique,the microstructure and grain boundary energy were analyzed quantitatively.As results,the welded joints of induction pre-heating LIHW contain relatively more martensite,and the grains are refined,which improves the tensile properties.However,after induction post-heating LIHW process,there appeared more bainite,large grains,and weld defects,the tensile properties were reduced.Thus,this paper selected the induction pre-heating LIHW as optimization process to conduct the following research.In the research of welding formation in LIHW process,the result,which indicates LIHW is better than laser welding(LW),was obtained from the analyses of weld geometry and microstructure formation.Firstly,by observing the welding stability,the influences of inductor output power on the geometry forming of welded joints were analyzed: due to the electromagnetic induction and keyhole penetration state after the induction coil was fed into alternating current,the plasma plume density reduced,the centroid became lower,the absorption and utilization efficiency increased,thus,with the increasing inductor output power,the variation periods were accelerated,weld defects were suppressed,the width and length of molten pool increased.Then,the thermal cycles of LW and LIHW were obtained,its effects on microstructure formation were analyzed.Based on the observing of microstructure,LIHW joints contained more ferrite and less martensite,which will decrease the microhardness and improve the tensile properties.According to the tensile fracture morphology of the specimens with symmetry grooves,the ductile fracture mode was mainly observed in the LIHW joints,and the brittle fracture mode was mainly observed in the LW.Furthermore,the impact energy of LIHW joint is much larger than LW.For investigating the fatigue performance,the stress ratio R=0.1 was selected to test fatigue specimens with symmetrical notches under the mode of tensile fatigue loading.The fitted S-N curve of laser-induction hybrid welding is above the fitted S-N curve of laser welding.At the same time,the fatigue fracture morphologies of LW and LIHW were observed at the stress amplitude of 108 MPa and 144 MPa respectively.It was found that the ductile fatigue area of LIHW is larger than that of LW,and the brittle fracture area in LIHW is smaller than that of LW.Thus,the LIHW has the ability to improve the fatigue performance of weld joints.In terms of corrosion properties,corrosion tests based on electrochemistry test of electrokinetic potential polarization was conducted.Through the analyses of polarization curve(corrosion potential,corrosion current density,corrosion velocity and grain boundary),corrosion surface morphology(pitting and rust layer)and element distribution,the corrosion performances of LIHW S690 QL steel were analyzed.The corrosion resistance of LIHW WC was found better than LW WC and base metal,and it presented increasing tendency with increasing inductor output power.In conclusion,compared with the LW process of S690 QL steel,LIHW process can improve the weld forming,mechanical properties and corrosion resistance of S690 QL steel welded joints.