Laser-induced breakdown spectroscopy of scaled steel samples taken from continuous casting blooms

Abstract

To analyse continuous casting steel blooms a removal of non-representative surface layers is required prior to the analysis. In this work, an optimized process is developed to ablate such layers and to analyse the bulk material underneath with laser-induced breakdown spectroscopy (LIBS). A high ablation rate is crucial since the time slot for an inline analysis is limited, e.g. to <1 min. To get a deeper understanding of the material structure between bulk material and surface, samples are sawed out of steel blooms. The samples are analysed in lab scale experiments including LIBS measurements and cross-section polish methods. These studies show that the surface layers may consist both of oxides and metallic layers and typically have thicknesses from 200 μm to 600 μm each. The ablation behaviour of the oxide differs significantly from that of the metallic layers. An operation scheme for inline material identification is worked out to perform ablation and analysis with a single laser source. During the ablation phase and the subsequent measurement phase the laser source is operated with individually tailored parameters. A total penetration depth exceeding 1 mm in steel can be achieved within 20 s of ablation. Thereby the influence of non-representative surface layers on the following LIBS measurement can be suppressed to a large extent. For chromium, relative root mean square errors of predictions of less than 13% were achieved on high alloy samples with up to 16 m.–% Cr and on low alloy samples with Cr contents below 2 m.–%

LIBS analyses for industrial applications – an overview of developments from 2014 to 2018

“…2,32 In the rst phase a scale layer thickness of 200-600 mm has to be penetrated. Within 20 s an effective crater depth of >2 mm in scale material is achieved.…”

Crosstalk effects of the surface layers of metallic samples on laser-induced breakdown spectroscopy measurements

“…It is obvious that a potential solution is the local ablation of the surface layer by the laser beam itself. To this end, a LIBS method and setup was developed and studied to analyse scaled steel blooms [12,13].…”

Improved Analysis of Manganese in Steel Samples Using Collinear Long–Short Double Pulse Laser-Induced Breakdown Spectroscopy (LIBS)

“…In recent years, laser-induced breakdown spectroscopy (LIBS), as one of the analytical techniques for the steelmaking process, has been widely studied because of its potential for in-line analysis. 1,2 Various papers have been published to report the applications of LIBS in the steel industry, such as the measurements of solid steel, 3–9 liquid steel, 10–12 slags, 13–15 oxides, 16–18 rapid in situ analysis, 19–21 etc . One vital subject among these studies is the analytical performance of LIBS for the industrial application.…”

“…42 The two-phase measurement scheme with first cleaning long pulses and the second analysis laser pulses was applied to the analysis of as-cast layers on a steel bloom. 8 However, the long–short DP-LIBS method studied in the present work employed the simultaneous combination of long and short pulses. A long laser pulse with the duration in a tens of microseconds time scale and a Q-switched short pulse with the duration in a nanosecond time scale were both involved in the plasma generation and evolution processes.…”