ADVANCED MATERIALS & PROCESSES | MAY/JUNE 2025 15 Fig. 1 — (a) Digital camera image of the weld seam within the material and (b) light microscope image showing a particle embedded within acicular ferrite laths in the melt zone, highlighted with an orange arrow. The laths appear to originate from the particle, indicating a potential nucleation site. in six mostly visible laths, highlighted with black arrows. The identified region was then marked and documented. Further observations were subsequently performed using electron microscopy techniques as shown in Fig. 2. First, using the SEM it was confirmed that the particle seemed to be embedded within the matrix. Afterwards, EBSD analysis was performed to confirm the existence of acicular ferrite in the particle’s vicinity resulting in Figs. 2a and 2b. For this purpose, misorientation angles were then obtained and compared to literature values according to a method proposed by Gourgues et al., which allowed a clear differentiation between acicular ferrite, which is generally characterized by an absence of lowangle misorientation boundaries and a high proportion of misorientation angles around the NW/NW orientation relationship, and other possible microstructure constituents like upper bainite[6]. The misorientation angles shown in Fig. 2c confirmed the acicular ferrite microstructure, exhibiting a small occurrence of low-angle misorientation angles. The increase in the proportion of misorientation angles around 30° and above has also been observed in other studies[7]. However, at this stage no definitive explanation can be provided for these data points. Due to the particle’s unique (a) configuration, which was supposedly split in half with its midsurface facing upward, EDS measurements could be performed without significant topographic distortions. The results of these measurements are shown in Fig. 3. (b) Fig. 2 — (a) SEM image illustrates the particle, highlighted by an orange circle, within the steel matrix; and additional EBSD image showing the di erent lath orientations as cubes around the particle. The surrounding region is shown in part (b) with the previously shown region in part (a) in the black square. The misorientation angles measured within region (b) are shown in (c). A direct comparison with data adapted from Gourgues et al.[6] emphasizes the acicular ferrite phase structure, with a small proportion of low-angle misorientation angles. A more narrowly defined region also confirmed this finding. (a) (b) (c)
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