Laser Powder Bed Fusion (L-PBF) is an additive manufacturing technique that utilizes a laser source to selectively fuse metal powder together layer-by-layer to produce 3D components. This method has gained interest due to its ability to produce near net-shape parts while achieving high material utilization with reduced lead times. Despite this, the number of alloys available for the process remains limited, with few alloys tailoring their composition to match the unique processing history of L-PBF.

Structural steels are gaining popularity in L-PBF due to their combination of strength, toughness, and wear resistance, making them sought after for automotive and structural applications. Although they are difficult to process due to their high carbon content, the presence of carbon also improves the wettability and flow of the melt pool, making it easier to avoid defects such as lack of fusion. This indicates that adequate adjustment of the carbon content is important to optimize the processability of structural steels for L-PBF. However, the effect of carbon on the melt pool has only been examined via ex-situ studies and to better understand this phenomenon in-situ experiments are required.

In this work, in-situ x-ray imaging measurements were conducted at the European Synchrotron Radiation Facility. These measurements were carried out on carbon steels with compositions between 0 to 1.1 wt.% C using the mini-SLM, which is a miniaturized L-PBF device specifically designed for use at large-scale facilities. These experiments involved the exposure of single tracks for each of the examined compositions. To follow the dynamics and fluid flow within the melt pool tracer tungsten particles added into each of the examined powders. These in-situ measurements were corroborated to melt pool simulations from the AM module of ThermoCalc software.

From these measurements, it was possible to observe in-situ the changes in the melt pool dynamics and fluid flow as a function of the carbon content. The further correlation of these results to melt pool simulations made it possible to predict the conditions within the melt pool prior to processing. From these results, one can better tailor and thus specifically develop the composition of structural steels so they take advantage of the unique processing history of L-PBF.