Characterization of Titanium and Niobium Carbonitride Precipitates in Steel

Single-Particle Mass Spectrometry of Titanium and Niobium Carbonitride Precipitates in Steels

This contribution demonstrates how multi-element single particle (me-sp) analysis using TOFWERK‘s inductively coupled plasma time-of-flight mass spectrometer (ICP-TOFMS, icpTOF) can be applied to measure particle size, particle size distribution, and particle composition of titanium and niobium carbonitride precipitates in steel.

Hegetschweiler, A.; Borovinskaya, O.; Staudt, T.; Kraus, T.
Analytical Chemistry 2018
DOI:10.1021/acs.analchem.8b04012

Small amounts of some metals precipitated during the steel production process can either improve or degrade the mechanical properties of steel. Therefore, characterizing the composition and particle size distribution of these precipitates is extremely important for the optimization of steel quality.

This contribution demonstrates how multi-element single particle (me-sp) analysis using TOFWERK‘s inductively coupled plasma time-of-flight mass spectrometer (ICP-TOFMS, icpTOF) can be applied to measure particle size, particle size distribution, and particle composition of titanium and niobium carbonitride precipitates in steel.  These precipitates are of critical importance in the production of microalloyed steels.

The findings of this study can be summarized as follows:

  • Particles must be extracted from the whole steel prior to the analysis and the applied extraction procedure requires careful optimization, which was conducted in a separate study
  • Particle size and size distributions obtained with multi-element single particle ICP-TOFMS are in accordance with the results from scanning transmission electron microscopy (STEM), which is one of the most commonly applied methods for the characterization of steel precipitates
  • Multi-element single particle ICP-TOFMS provides higher statistical relevance, because it can measure a few thousand particles in 1 min run, whereas even a highly experienced STEM operator can analyze only a few hundred particles within 2 working days
  • Multi-element single particle ICP-TOFMS provides the absolute mass content of Ti and Nb in individual niobium and titanium carbonitride particles that is tricky to obtain with STEM without a sophisticated calibration procedure
  • After accounting for all particle losses during the extraction and the ICP analysis, at least 12% of the alloyed Nb was found in pure Nb carbonitride particles
  • “Large” TiNb particles contain at least 23% of the alloyed Nb which does not contribute to mechanical strengthening and indicates potential for improvement of the production process

The paper also discusses the advantages and disadvantages of me-sp-ICP-TOFMS in comparison to STEM and potential of the technique for other precipitate systems in steel.