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.

A nickel-based filler wire, Inconel 82, was applied to weld a high-silicon steel plate with a chemical composition in wt% of 2.6 Si, 0.5 Al and Fe balance. The chemical composition of the heterogeneous weld bead was deviated from that of the conventional alloy due to incomplete mixing/convection between the filler wire and base metal in the weld pool. The microstructure of the weld bead was examined in greater depth by FESEM/EBSD, EPMA/WDS and STEM/EDS in the experiment. The heterogeneous weld bead was primarily composed of austenite and martensite, and mainly governed by the Ni concentration. A Schaeffler diagram based on the ratio of Cr and Ni equivalents in the selected positions of the weld bead was used to predict the structure and phase(s) of the Fe-based weld bead. A methodology for the analysis of a weld metal with an unconventional alloy composition has been proposed in the study.

It is important to control the microstructure and properties of a weld for the continuous production of silicon steel sheets. Post-weld heat treatment (PWHT) can be applied to adjust the weld properties; however, research on its application to silicon steel weldments remains limited. This study investigated the microstructure and hardness evolution of the weld after PWHT for high-silicon steel, with Inconel 82 used as the filler material. The weldment contained FCC phase and BCC phase regions, and PWHT were conducted at 520, 620, 720, and 920 °C for 8 h. Experimental observations indicate that G-phase precipitations in FCC phase could increase its hardness, and it peaked at 620 °C with an average hardness of 259 HV. By contrast, the BCC phase region was subjected to martensitic transformation and its hardness increased from 305 to 335 HV after PWHT at 920 °C. To elucidate microstructure evolutions, CALPHAD-based simulations successfully predicted BCC to FCC phase transformation at 920 °C, peak G-phase precipitation at 620 °C, and elemental diffusion at the BCC and FCC interface. The findings indicate that CALPHAD-based simulations offer a robust approach that can be extended to understand the effect of PWHT.