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To control the steel composition during production in steel works, samples are taken from the melt. After solidification, the samples exhibit scale layers of about 0.1-1 mm thickness. At present, for analysis of the bulk composition, e.g. by optical emission spectrometry using arc/spark excitation, the scale layer is removed by grinding or milling and afterwards the prepared sample is measured. In this study we use multi-pulse bursts of a Nd:YAG laser at 1064 nm wavelength to ablate the scale layer of low-alloy steel samples locally in a first step, and the bulk material is analysed in a second step by laser-induced breakdown spectrometry (LIBS). With a LIBS set-up including a Paschen-Runge spectrometer, detection limits below 10 µg g(exp -1) are determined for elements such as C, P, S, Al, Cr, Cu, Mn and Mo. Production control samples with one original scale side and one ground side are analysed on both sides and the analytical results are compared. The values correlate with a coefficient of determination greater than 0.99 averaged over the observed elements

The sensitivity of laser-induced breakdown spectroscopy of solid samples depends on the number of ablated and excited analytes. Laser ablation of solid samples can be enhanced by using collinear multiple laser pulses, for example double or triple pulses, rather than single laser pulses with the same total laser pulse energy. The ablation rates and the plasma conditions are affected by the ambient gas. In this study laser ablation was examined by varying the interpulse separation of the multiple pulses, within double and triple-pulse bursts, and the gas mass density at constant gas pressure. Different ambient gases and gas mixtures consisting of argon, oxygen, and nitrogen were used to study their effect on ablation rates. In a pure argon atmosphere (99.999% v/v Ar) the ablation burst number required to penetrate a steel plate of thickness 100 microm is reduced by a factor of approximately six by use of triple-pulse bursts with a symmetric interpulse separation of 15 micros rather than single pulses with the same total burst energy of 105 mJ. For double and single pulses the factors are 1.6 for Ar and 2.8 for synthetic air. Analyte lines are 4 to 8 times more intense if an argon atmosphere, rather than air, is used.

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