In situ analysis of steel melt by double-pulse laser-induced breakdown spectroscopy with a Cassegrain telescope

Abstract

A laser-induced breakdown spectroscopy (LIBS) system combining a Cassegrain telescope and a double-pulse laser mode was developed for the in situ analysis of steel melt. Optical- and electrical-related devices were sealed in an enclosed box away from the high-temperature steel melt surface. Connected to the box by a flange, a long hollow steel tube was used for the laser and plasma emission transmission path. At the tip of the steel tube, a refractory lance that can withstand high temperatures was immersed into the molten steel surface to pass through the surface slag layer. The designed optical structure successfully keeps the photoelectric-associated system components away from the high-temperature environment, thus reducing the complexity of system protection and maintenance. The signals obtained from single-pulse and double-pulse LIBS were comprehensively compared; the effect of argon blowing on spectral stability was analyzed; and the quantitative analysis of Si, Mn, Cr, Ni and V in molten steel samples was evaluated using both a univariate model and a partial least squares (PLS) model. The relative root mean square error of prediction (RMSEP) values and average relative standard deviations (RSDs) of the PLS model were approximately 5% and 2%–3%, respectively, both of which are less than those of the univariate calibration model. The sealed LIBS setup was also transferred to a steel plant for application testing, and the obtained accuracy approached the plant's accuracy requirements. Furthermore, quantitative analysis of carbon was also achieved on the basis of the PLS models. These results demonstrate that the developed system is promising for the in situ analysis of melt steel in the steelmaking industry.