The Dilution Effect in High-Power Disk Laser Welding the Steel Plate Using a Nickel-Based Filler Wire

Abstract

High-power disk laser welding a steel plate using the Inconel 82 (IN82) filler wire with a 1.2 and 3.0 m/min feeding rate has been investigated in the experiment. The rapid thermal cycle combined with convection induced by the keyhole mechanism in laser welding results in the rapid solidification of the fusion zone (FZ). However, the microstructure of the FZ is not homogeneous at the macroscopic scale. The dilution of the FZ is important in determining the final microstructure of the weldment. For the specimen with a 1.2 m/min wire feeding rate, a lower amount of Ni-based IN82 filler is introduced into the weld pool, and the dilution of the FZ is between 65% and 100%. The BCC structure with high density boundaries dominates the entire FZ. For the specimen with a 3.0 m/min wire feeding rate, part of the filler melt is trapped on the top of the weld pool, and solidified into austenite alloyed with a Ni concentration above 15 at%. The range of dilution in the FZ with a 3.0 m/min wire feeding rate is decreased to 50–90%. There are hot cracks initiated/propagated along interdendritic austenite and in the austenite free of boundaries. Boundaries, especially for high-angle ones, in the BCC structure retard hot crack propagation in the FZ. The application of quantitative chemical analyses of Fe or Ni concentrations in the weldment provides a good approximation in evaluating the dilution of the FZ in laser welding. The methodology proposed in this study shows potential to obtain the dilution of any specific location in the FZ for industrial application in the future.

Microstructure of Butt Joint of High-Silicon Steel Made Using CO2 Laser Welding and Inconel 82 Filler

“…Therefore, the phase/structure of the WB was not uniformly distributed after solidification. According to the aforementioned results, the redistribution of Ni in the WB was mainly driven by convection and dilution of the BM into the weld pool, and it was strongly related to the formation of the phase/structure of the WB [14].…”

“…However, the characteristics of extremely short interaction time during the laser welding resulted in incomplete mixing of the filler wire and the BM in the weld pool. The dilution of the heterogeneous WB was not homogeneous after solidification [14]. Therefore, the phase/structure of the WB was not uniformly distributed after solidification.…”

“…However, the convection of the molten weld pool is incomplete due to the rapid thermal cycle of laser welding. Therefore, the elemental distributions in the weld bead (WB) are not uniform on a macroscopic scale [14]. The chemical composition of the heterogeneous WB will be quite different from those of the filler wire and base metal.…”

“…The chemical composition of the heterogeneous WB will be quite different from those of the filler wire and base metal. The chemical composition of the WB is strongly related to the dilution of the BM, and it plays a crucial role in the microstructure of the solidified WB after laser welding [10,11,14].…”

“…The microstructure of the heterogeneous WB of a ferrous BM welded with the nickel-based IN82 filler wire is quite complex because of the phase transformation of the WB is involved in the fusion zone. Austenite, ferrite and martensite can all be observed in the WB, depending on the dilution of the weld pool [14]. The Schaeffler diagram illustrates the microstructure of a welded stainless steel with the aid of Cr/Ni equivalents [10,11].…”