We introduce a new method for the characterization of particles extracted from steels. Microalloyed steels were dissolved to extract niobium and titanium carbonitride particles, which are of critical importance for the mechanical properties of the steel. The size distribution and chemical composition of the particles were analyzed by single-particle inductively coupled plasma mass spectrometry and compared to results from electron microscopy. Mass spectrometry rapidly provided data on a large number of particles (>2000 in 1 min) and indicated two particle populations that differed in size and composition: smaller particles contained only niobium, whereas larger particles contained both niobium and titanium. Electron microscopy of a much smaller number of particles confirmed the results and indicated that the larger particles had complex, overgrown structures. The combination of single-particle mass spectrometry and electron microscopy enables a better understanding of the precipitation processes that form the particles during steel production at different stages of the thermomechanical-rolling process. A better understanding of the processes helps to improve the rolling process in order to exploit the alloying elements optimally.