LIBS applications for production control in steel industries

Volltext: Recent progress in sensitivity connected with an advanced design of equipment enable the laserinduced breakdown spectrometry (LIBS) to meet the requirements of real-world applications. Elemental analysis for production control in steel industry is one example. In this contribution, the state of the art is summarized and applications such as the identification of steel products, the analysis of liquid steel and the fast determination of steel cleanness -are described. For the final inspection of the steel grade of pipe fittings, two machines based on LIBS were developed and installed in a production line. The steel grade is of decisive importance if the pipe fittings are exposed to corrosive fluids, e.g. in the oil and chemical industry. In order to avoid a leakage due to corrosion with considerable consequential costs and possibly catastrophic environmental damage, one has to assure that always the proper steel grade is applied and no accidental mix-up occurs. According to product liability the producer of pipe fittings is interested to perform a 100% inspection of his products. The machines installed in Germany and Malaysia control each pipe fitting automatically within 2 seconds. An expert system was developed for the classification of up to 30 steel grades from the measured data. More than 400 000 pipe fittings were inspected during the last 18 months, and the experience on the routine operation of the machines is reported. Increasing standards for steel qualities require advanced methods of steel analysis, especially during secondary metallurgy in steel works. The fast multi-elemental laser analysis of liquid steel has the potential to replace the spot checks of today by a more representative measurement. Preconditions are the sufficient analytical performance, i.e. limits of detection (LOD) of less than 10 æg/g for most of the relevant elements, and the reliable optical access to the steel melt. By using a sensitivity-enhanced LIBS design we measured LOD values in the vicinity of 10 æg/g and below for the crucial elements C, P, S as well as for other elements such as Cr, Ni, Mn and Si. Furthermore, we report about operational tests of an immersion lance which permits the optical access to the melt for the laser analysis. Operational periods of more than 4 hours with the lance immersed into a 100-kg steel melt at a temperature of about 1630øC and running laser analysis were demonstrated successfully with this equipment. The rapid determination of steel cleanness is important in the production of high-quality steel for springs, thin foils and wires, because inclusions of e.g. A12O3 or SiO2 with typical grain sizes of 0.1 - 100 mu m have a deleterious effect on the physical properties of steel. For product development, process control and quality assurance, a fast method is required to identify and quantify such inclusions. For this application, a scanning LIBS apparatus was developed consisting of a diodepumped laser, a Paschen-Runge vacuum spectrometer, a fast multi-channel integrating electronics, translation stages and an automatic control for most operations. The laser allows repetition rates of up to 1 kHz and, due to its good beam quality, small focal spot sizes are possible resulting in a spatial resolution of 20 æm. In summary, it is demonstrated that LIBS is a versatile tool for steel analysis in production control and the technique is no longer restricted to laboratory use only