Research On The Welding Procedure And Weld Microstructures And Properties Of High Strength Steel Thick Plate Welded By Laser Welding With Filling Wire

This article has mainly studied the laser welding with filling wire in the narrow gap ofthe thick plate. A special wire feeding system and gas shielding system was designed for thenarrow gap, making it possible to put the wire guide tube and gas guide tube into the narrowgap. At the same time, the angle and the height of the wire guide tube and gas guide tubecan be separately adjusted easily. The stability of the wire feeding process and the gasprotecting effect are improved.Research on the welding parameters of the laser welding with filling wire is carried outwith the material of Q345A low alloy high strength steel. Laser autonomous welding on thesurface of the testing plate, Laser welding with filling wire on the surface of the testing plate,Single-pass laser welding with filling wire in the narrow gap and Multi-pass laser weldingwith filling wire in the narrow gap were carried out in turn. The influence of the weldingparameters on the weld formations was analyzed. The welding parameters were optimized.The results show that when the root face width is2mm and the groove angle is6degree, itgets the highest welding efficiency and best welding quality. The weld formation for theMulti-pass laser welding with filling wire in the narrow gap is the best when the laser poweris2.2KW, welding speed is0.1m/min, wire feeding speed is0.75m/min, gas flow is10L/min and gas guide tube angle is6degree. The heap of the single-pass weld is about3mm. If the wire feeding speed goes faster, defects like porosity and incomplete fusionwould occur inner the weld.The30mm thick10Ni3CrMoV high strength steel was welded by the optimizedwelding parameters through multi-pass laser welding with filling wire in the narrow gap.The microstructure of the joint was analyzed. It shows that the microstructure of the weld ismainly composed by granular bainite and some fine lath martensite. The microstructure ofthe coarse grain zone of the heat affected zone is mainly composed by large lath martensiteand the microstructure of the fine grain zone of the heat affected zone is mainly composedby fine lath martensite and a little granular bainite.The micro-hardness test of the10Ni3CrMoV high strength steel joint shows that thehardness of the weld zone welded by laser autonomous welding is higher than the weld zonewelded by laser welding with filling wire, but the hardness of the coarse grain zone of heataffected zone is just the opposite. Under the influence of the second welding thermal cycle, the hardness of the weld zone gets higher and the hardness of the heat affect zone gets lowerfor the joints welded by laser welding with filling wire. The highest hardness of the heat affectzone is334HV and the highest hardness of the weld zone is275HV. The fractures of thetensile specimens all located at the base metal area, it means that the tensile strength of theweld joints is higher than the tensile strength of the base metal.