Study of laser-induced breakdown spectroscopy to discriminate pearlitic/ferritic from martensitic phases

The 20G steel has been widely used for boiler heat exchange surface. In this paper, we use laser-induced breakdown spectroscopy to analyze steel samples with different microstructures. The plasma parameters (e. g. line intensity, temperature, and ablated crater) of different microstructures have been studied and compared with each other. Our results reveal that the difference of ionic Fe lines is more obvious than atomic Fe lines between pearlite/ferrite and martensite. The ablated volume of pearlite/ferrite is distinctly larger than that of martensite, whereas there is no significant difference between the plasma temperature of pearlite/ferrite and that of martensite. Additionally, we employ principal component analysis method to differentiate these samples, and study the performance of different wavelength ranges (200-290 nm, 288-393 nm and 391-480 nm). The results show that the plasma spectra of pearlite/ferrite and martensite can be separated completely by PC1 in the range of 200-290 nm. The investigations indicate that LIBS may be applied not only as an elemental analytical technique but also a new way to determine the microstructure changes of steel samples. (C) 2010 Elsevier B.V. All rights reserved.