Rapid in-situ analysis of liquid steel by laser-induced breakdown spectroscopy

Abstract

Laser-induced breakdown spectroscopy (LIBS) denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma allow a quantitative chemical analysis of the target material. LIBS is a fast, non-contact method allowing large working distances between the sample under investigation and the detection system. These properties make LIBS applicable to process control in metallurgy. We describe an apparatus designed for rapid in-situ analysis of solid and molten metals at variable distances of up to 1.5 m. A variable lens system allows compensation for varying positions of the liquid steel surface. The LIBS signal is guided by a fiber optic bundle of 12-m length to the spectrometer. Analysis of an element's concentration takes 7 s. Laboratory experiments using an induction furnace showed that the addition of admixtures to liquid steel results in rapid response of the system. Results including the in-situ monitoring of Cr, Cu, Mn and Ni within certain concentration ranges are presented (Cr: 0.11–13.8 wt.%; Cu: 0.044–0.54 wt.%; Mn: 1.38–2.5 wt.%; Ni: 0.049–5.92 wt.%).