Improved production control through rapid characterisation of non-metallic inclusions in steel

For fast steel cleanness characterisation, the application of laser OES has been investigated as an appropriately quick analytical tool. Within the project duration of three years some fundamentals of signal generation referring to metallic and non-metallic phases have been studied to distinguish between various concentrations and types of inclusions in steel. Statistical approaches and models have been formed to interpret the data collected. The identification of inclusion types has been run by focusing on coincidences of significantly enlarged signals in different inclusion-related element channels including the light elements (C, N, O, P, S) in the vacuum UV range down to 130 nm. The results of the laser OES measurements have been correlated with those from electron microprobe (EPMA), optical microscopy and chemical isolation methods for different steel grades as well as for synthetic samples containing well-known concentrations of defined inclusion types. Two- and three-dimensional mapping has been carried out by single or multiple scanning of the area of interest. Some basic phenomena of material removal have been studied by observing the laser pulse craters induced under different conditions. A number of experimental set-ups depending on the laser source and the focusing optics have been tested, for example in terms of spatial resolution and sensitivity of the method. Grinding and milling has been compared for preparing the sample finishes for the laser OES measurements.