Non-metallic inclusions (NMIs) in steel have a detrimental effect on the processing,
mechanical properties, and corrosion resistance of the finished product. This is
particularly evident in the case of macroscopic inclusions (>100 μm), which are rarely
observed in steel castings produced using state-of-the-art technologies, whereby casting
parameters are optimized towards steel cleanliness, and post-treatment steps such as vacuum
arc remelting (VAR) are used, but frequently result in the rejection of the affected
product. To improve production processes and develop effective countermeasures, it is
essential to gain a deeper understanding of the origin and formation of NMIs. In this study,
the potential of elemental and isotopic fingerprinting to trace the sources of macroscopic
oxide NMIs found in VAR-treated steel ingots using SEM-EDX, inductively coupled plasma
mass spectrometry (ICP-MS), laser ablation ICP-MS (LA-ICP-MS), and laser ablation multicollector
ICP-MS (LA-MC-ICP-MS) were exploited. Following this approach, main and
trace element content and 87Sr/86Sr isotope ratios were determined in two specimens of
macroscopic NMIs, as well as in samples of potential source materials. The combination of
the data allowed the drawing of conclusions about the processes leading to the formation
of these inclusions. For both specimens, very similar results were obtained, indicating a
common mechanism of formation. The inclusions were likely exogenous in origin and
were primarily composed of calcium–aluminum oxides. They appeared to have undergone
chemical modification during the casting and remelting process. The results indicate that
particles from the refractory lining of the casting system most likely formed the