New developments for the quantification of non-conductive materials (slags, inclusions) in the steel industry by optical emission spectrometries (laser, spark)

The technological progress made in various industrial sectors (automotive, etc.) has increased the requirements on steel product quality. At the same time, the competition on the market has made it a necessity to decreasesteel production cost, while improving process control and quality. Today, XRF and spark-OES are respectively used to perform slag and steel analyses. Spark source OES has been developed intensively during the past years, leading to the use of pulse discrimination analysis (PDA-OES) to provide information about metal desoxidation. The aim of these works is to develop a method for the fast industrial quantification of slag and inclusion analysis by Laser-OES and Spark-OES. Results obtained through earlier studies concerning the source parameters, the interaction between energy and matter, and the quantification of inclusions (PDA-OES and laser) will help improve the models developed for inclusion characterization. This method will be applied on industrial samples to confirm its on-site applicability. In this research, two main types of steel grades are considered: - Low carbon steel grades and their associated slags. These samples, due to the interest of the low carbon steel industry are used for inclusion characterization both by spark and laser techniques. - Stainless steel grades, mainly considered for laser inclusion characterizations. The results obtained for these different steel types can be applied more largely, taking into account the adaptation of the developed analytical process. At the end of this research, we can conclude that some degree of consistency has emerged from the various inclusions content assessment methods considered in this project (chemical analysis, optical emission spectrometry and electron microscopy with EDS analysis). Results obtained with the Optical Spectrometer (Spectro, ARL) on liquid steel samples substantiate this conclusion and suggests an indirect determination of oxygen by PDAOES. The PDA-OES technique validated by wet chemistry analysis allows the steel manufacturers to obtain a complete overview of the quality of their products. These methods applied to different steel grade provide crucial information on steel cleanness. This fact is especially outstanding when the characterization of large areas or volume is required, as an example. Calibrations have been developed on different elements such as Al, Ca, Mg or Ti to quantify inclusion contents by PDA-OES techniques. The two sources (Laser and Spark) have been studied. The main difficulties are observed for element, which are not soluble in steel such as Ca or Mg. For those elements, the developed calibration curves are limited. For Aluminium, as an example, calibration curves are easier to define, using samples containing various content of soluble Al. The main problem to establish calibration curves is due to the heterogeneous distribution of the considered elements in the samples. This is particularly true when inclusions particles are relatively large. This is a limiting factor to define and to dispose satisfying calibration samples for cleanness quantitative analysis. An other very important result is the ability of the PDA-Spark-OES technique to be applied in the same sequence as bulk analysis during steel making control analysis, on an unique sample.