Non-metallic inclusions (NMIs) are microscopic particles (size range between 1 and 15 µm) inside the steel which inevitably form during steel production. Their exact formation and modification in the different production steps are not entirely clarified by today. Depending on the steel grade, NMIs affect the physical and chemical characteristics of the final products. Tracing techniques allow for tracking the sources of interfering particles and hypothesis the formation of single inclusion types over the process.
Two different tracing approaches have been investigated in this study. For the first approach, the rare earth element (REE) fingerprint in auxiliaries (e.g., casting powder, slag former, aluminum granules for deoxidation), clogging layer, and NMIs are determined. The REE patterns of the individual substances based on the REE content measured by ICP-MS are compared. Hence, the potential source of interfering inclusions can be determined since each substance is expected to have a unique REE fingerprint. An alternative and novel approach uses enriched stable isotopes to identify the source of NMIs. For this approach, which, until now, has not been applied in the field of metallurgy, the isotopic composition of one potential source of interfering NMIs is modified to a significantly different composition compared to other sources of the same element. Thus, a characteristic and unique tag is conferred on a potential input source of an NMI. Consequently, it is possible to track the evolution of these NMIs over the process by determining the isotopic ratio of single particles using spatially-resolved laser ablation (LA)-ICP-MS followed by isotope pattern deconvolution during data reduction.