Study Of Microstructure And Mechanical Properties In API X80 Line-pipe Steels Laser-MAG Hybrid Welded Joint

With the extensive application of X80 steel, it has great significance to carry out high-strength steel plate butt welding test. In order to comprehensively grasp the thick plate of laser-arc hybrid welding technology and performance, this paper make the topics of X80 high-strength steel plate laser-arc hybrid welding technology for basic research. Hybrid welding using optical fiber laser and MAG arc as heat source to achieve a complete high-strength steel plate butt weld root of Welding. The welded joints open V-groove, blunt the edge thickness of 6mm. There are five welding station, flat position welding, inclined welding, vertical position welding, inclined-overhead welding and overhead welding. The microstructure and mechanical properties of this five welded joints have also been studied.Through the five-station laser-MAG welding experimental research, each station obtained the optimal welding parameters. The optimal parameters of flat welding is described as below:the power of laser is 3500W; the defocusing amount is 0; the speed of the shielding gas is 301/min; the shielding gas composition by 18%CO2 and 82%Ar; the distance between laser and wire is 5mm; the gap between the two plate is 0.6mm and the arc average current is 220A. The other several welding stations have the same optimal parameters. It is described as below:the power of laser is 3800W; the defocusing amount is 0; the speed of the shielding gas is 301/min; the shielding gas composition by 18%CO2 and 82%Ar; the distance between laser and wire is 0; the gap between the two plates is 0.6mm and the arc average current is 220A.The microstructure of the heat-affected zone and the weld in five welding bead station has also been studied. As can be seen from the results, welding station has little impact on the microstructure. The types of microstructure of the heat-affected zone in each welding station are basically the same, mainly constituted by a variety of ferrite. The microstructure of welding bead is mainly constituted by acicular ferrite. In addition, five welding stations on the mechanical properties of welded joints have been studied. The five kinds of joints were carried out tensile test, Charpy impact testing and hardness testing. Summing up all the kinds of test results, concluded that the mechanical properties of the flat position welding is best.