Rapid sorting of stainless steels by open-air laser-induced breakdown spectroscopy with detecting chromium, nickel, and molybdenum

Laser-induced breakdown spectroscopy (LIBS) is a promising method for rapid determination of compositions of stainless steels in steel scrap. LIBS is widely known as a method for elemental analysis that enables a rapid determination. It has several advantages such that it can work under ambient pressure, and specimens can be tested without any pre-treatment such as acid digestion, cleaning, or polishing of surface of specimens. We applied a laboratory-build LIBS system for sorting of six types of stainless steels. The standard reference materials of JISF FXS 324-334, 335-343, and 344-349, which are respectively Fe-Ni, Fe-Cr, and Fe-Mo binary alloys, were employed for making calibration lines of them. Considering spectral interferences from emission lines of the iron matrix in these alloys, seven emission lines could be chosen. Longer gate width, shorter delay time, high stability of pulse laser energy, and more number of laser shots can decrease the fluctuation of emission intensity. Utilizing these parameters mentioned above, the sorting of stainless specimens by detecting chromium, nickel, and molybdenum could be achieved.