Rapid analysis of content and particle sizes of aluminum inclusions in low and middle alloy steel by laser-induced breakdown spectroscopy

Abstract

Non-metallic inclusions affect the mechanical properties of steels. Laser-induced breakdown spectroscopy (LIBS) has the advantages of simple sample preparation, fast analysis, and high spatial resolution. The content and particle sizes of aluminum inclusions in low and middle alloy steel were analyzed by LIBS. Signals of intensities that are higher than the threshold were generated by laser pulses on inclusions. The threshold was calculated cyclically (I¯+ks), where I¯is the average intensity, k is a coefficient that is related to the confidence probability, and s is the standard deviation. A content analysis model for aluminum inclusions was established and relates to the number and intensity of the signals. The root mean square error of calibration of inclusion contents for calibration samples is smallest when k = 2.2. The content of aluminum inclusions in the test samples was calculated with k = 2.2, which agrees with that of acid-insoluble aluminum. The relationship between the intensity that was generated by laser pulse on an aluminum inclusion and particle size was deduced, and a quadratic polynomial fit of net intensity and particle size was used. Particle size ranges of ≤3 μm, 3–5 μm, 5–7 μm, 7–10 μm, 10–15 μm, and ≥15 μm for test samples to which spectral signals that correspond to aluminum inclusions belong were determined. The percentages of aluminum inclusions in each particle size range that was obtained by LIBS correspond approximately with the results from scanning electron microscopy coupled with energy dispersive X-ray spectroscopy.