Evaluating Techniques for Identifying Isotopically Spiked Non-Metallic Inclusions in Steel

Description

Non-Metallic Inclusions (NMIs) are primarily microscopic particles, typically in the size range of a few micrometers, present in steel. These NMIs are inevitably formed during the steelmaking process and significantly influence both the chemical and physical properties of steel. Given their impact, it is crucial to study their formation and modification. By understanding the origin and behavior of NMIs during production, targeted countermeasures can be implemented to reduce the number of detrimental NMIs in specific steel grades. As a result, downtimes in the steelmaking process can be minimized and the product quality can be enhanced. The implementation of tracing techniques allows the identification of the origin of NMIs. One novel promising approach lies in stable isotope labelling. Due to the modification of the isotopic ratio of, for example, one component in the slag, it is possible to study the steel/slag/refractory system in more detail. In the present study, the MgO used in the slag was spiked using an enriched stable 26Mg isotope. By measuring the isotopic ratio of slag, refractory and NMIs, it was possible to identify whether NMIs were modified or originated by slag or crucible. Sensitive measurement techniques are required to determine the isotopic composition of slag and refractory as well as to evaluate the origin of NMIs.
Within this study, three analytical approaches were compared in terms of their applicability to measure the isotopic ratio in NMIs. The first analytical method was Laser Ablation - Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS), a fast analyzing technique with limited spatial resolution (1 – 50 µm). As the second technique, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was applied. This method has a minimum spatial resolution of 35 nm and, hence, enables an investigation of the entire spectrum in single atomic layers. Due to the coupling of ToF-SIMS to Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM/EDS), it is possible to obtain elemental and isotopic information about the investigated NMI. The third method is atom probe tomography, which has the highest spatial resolution and allows measurements on the atomic level. Here, only small parts of an NMI can be investigated since the analyzable sample size is only a few hundred nanometers in size. All three techniques successfully detected the 26Mg spike in the isotopically modified slag. Within this work, advantages as well as challenges of the applied analyzing methods are discussed.

Period	15 Sept 2025
Event title	FEMS Euromat 2025
Event type	Conference
Location	Granada, SpainShow on map
Degree of Recognition	International