INDUCED PLASMA SPECTROMETRY; IN-SITU ANALYSIS; HIGH-TEMPERATURE; ELEMENTAL ANALYSIS; GRADE TRANSITION; MOLECULAR BANDS; REAL-TIME; MOLD; LIBS; SAMPLES

Among the several controlling routines utilized in the steelmaking process, analytical operations during continuous casting are especially demanding due to the extreme environment of steel plants and the crude conditions of the steel surface at the exit of the casting system. This report presents how dual-pulse laser-induced breakdown spectroscopy (LIBS) can be used for the real-time monitoring of continuous casting sequences in a steel plant and the operations needed for detecting the separation between grades of close chemical compositions. Diverse dual-pulse laser conditions have been tested in order to improve the LIBS system performance. Apart from the scale layer formed by the oxidation of steel by the surrounding air, the presence of residues of mould powder on the steel surface tends to complicate the LIBS analysis as elements present in the powder such as manganese interfere with the steel components. LIBS data processing by discriminant function analysis has been demonstrated to be beneficial for the identification of steel transitions. Changes in steel composition as low as 0.20 percentage points Cr in a stainless steel sample containing above 17% of this element are detected by corresponding changes in Wilks' lambda values from 1.0 to 0.75 during the transition. Changes in the concentration of nickel are of minor relevance as its concentration on the steel surface at the time of continuous casting is depleted. For steel concentrations differing to a larger extent, differentiation of steel grades is straight, involving changes in Wilks' lambda values from 1 to below 0.1.

Laser-induced breakdown spectroscopy; Stand-off analysis; Solid aerosol detection; Steelshop atmosphere; Continuous casting line; Sampling rate;INDUCED BREAKDOWN SPECTROSCOPY; AEROSOL-PARTICLES; INTEGRATED IRON; AIR; TEMPERATURE; EMISSIONS; OXIDATION; ALUMINUM; SURFACES; ALLOYS

The analytical possibilities of laser induced breakdown spectroscopy (LIBS) to carry out in-situ and real-time detection and compositional characterization of aerosols in the atmosphere of a steelmaking factory, have been evaluated. To this aim, a compact and versatile dual-pulse LIBS analyzer, able to sample at distances up to eight meters, has been designed to work in these hostile industrial environments. Due to the discrete nature of the particulate matter, the particle sampling rate was less than 2.5% and 6% for single-and double-pulse regimes, respectively. An efficient statistical procedure, based on the calculation of standard deviations, is used to qualitatively characterize the elemental composition of the aerosol. Then, a conditional analysis based on the limit of detection, is employed to assess the elemental sampling rate. This experimental methodology has been used to evaluate the influence on the aerosol formed of the oxycutting process in a continuous casting machine producing steel slabs, revealing a strong presence of elements derived from the casting powder used in the production. Moreover, chromium, present in the steel cast, is detected in aerosol suspension in the steel shop. An increase in the concentration of particulate matter was expected when oxycutting was on. Single-pulse and dualpulse excitation modes are also evaluated.