Abstract Scope |
High energy density welding processes are used in many industrial applications, including the aerospace, defense, and medical products industries. Many of these applications require joint configurations that make post-weld inspection techniques difficult or impractical in highly critical components. Because of the inability to validate postweld quality, improving prediction capabilities and utilizing in-process monitoring to insure weld quality and structural integrity is crucial. In addition, understanding the effect of process conditions on the microstructure and properties in HED welds is needed to mitigate weldability-related concerns.
The objective of this work is to investigate the relationship between laser weld parameters and material properties to further understand keyhole evolution, weld pool development, and microstructural formation. Partial penetration, bead-on-plate laser beam welds were produced on stainless steel alloys using an ytterbium-doped fiber laser. Through the use of inline coherent imaging and a compilation of individual depth measurements, the vapor capillary geometry was reconstructed and compared for different parameters. The microstructural evolution was also investigated for six different stainless steel alloys with WRC-1992 Cr/Ni equivalencies ranging from 1.7 to 2.8, including 304L (UNS S30403) stainless steel (SS) and 2205 (UNS S32205) duplex stainless steel (DSS).
Process parameters significantly influenced the location of the keyhole relative to the process beam and the overall shape and width of the vapor capillary, which directly influenced the molten pool geometry, shape of the fusion zone, and discontinuity/defect formation. Longitudinal sections have shown a correlation between the keyhole position/angle and root porosity. Within a single weld, varying solidification directions stabilized multiple solidification modes which resulted in several as-welded microstructural morphologies. Also, equivalent ratios of ferrite and austenite were produced in high aspect ratio welds when the WRC-1992 Cr/Ni equivalency was near 2.2 relative to 1.7 for 304L SS and 2.7 for 2205 DSS. |