Recent advances of evaluation methods for non-metallic inclusions in steel

Methods for evaluation of inclusions in steel are reviewed in this paper. In characterization of inclusions in steel, it is required to measure their size distribution, composition and morphology as well as their amount. The size and amount of inclusions to be evaluated have been greatly reduced in ultra clean steel. On the other hand, a variety of oxides have to be analyzed in the oxide metallurgy where oxides are utilized as precipitation sites. Conventional methods such as chemical extraction and metallographic microscope observation have been improved or modified to meet these requirements. Applications of high frequency ultrasonic testing and fusion extraction using EB or cold crucible have been reported regarding evaluation volume or speed. Recent developments of other rapid methods including spark-OES, laser analyses and ESZ are also introduced.