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Effects of Various Active Fluxes on the Quality of Laser Welded Thick Stainless Steel Plates
D-B. Yan, S. XIE, L-F. MEI, Z-Q. LEI, X-F. Chang and Z-H. Wang

The effects of adding five active fluxes: SiO2; TiO2; Cr2O3; NaF; and CeO2 on the fibre laser welding performance of thick 304 stainless steel plates were investigated in depth. Welding samples coated with different active fluxes were tested and analysed from the following aspects: weld formation, joint microstructure, mechanical properties and elemental composition. These were then compared with the uncoated thick 304 stainless steel samples. The results demonstrated that the application of an appropriate type and thickness active flux was conducive to improving the weld formation of laser welded thick 304 stainless steel plates, increasing their penetration depth, refining their microstructure, and enhancing their mechanical properties. Of the studied fluxes, the SiO2 flux exhibited the most distinct effect of enhancing the weld surface morphology. The Cr2O3 flux was the most effective in increasing the weld penetration depth, refining the microstructure and enhancing the joint tensile strength. Besides, the hardness value of the heat affected zone (HAZ) and the weld zone (WZ) increased to the greatest extent. The TiO2 flux easily caused defects such as pore generation, resulting in the weakened tensile strength of weld; the Cr2O3 flux decreased the Cr content at the middle and bottom of the laser welds slightly. Apart from the aforementioned oxide and Cr2O3 fluxes, no other active fluxes had any significant effect on the elemental contents at the WZ.

Keywords: Fibre laser, 304 stainless steel, active flux, laser welding, tensile strength, microhardness, microstructure weld quality, heat affected zone (HAZ)

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