Application of Raman spectroscopy for the characterisation of synthetic non-metallic inclusions found in Al-killed calcium treated steels

The end-users of steel products continue to demand high-quality steels, and non-metallic inclusion is the most common parameter that relates to steel cleanliness assessment. Depending on the type and content of non-metallic inclusion found within steel matrix, it can be considered detrimental to the steelmaking process, the final steel product and quality. To minimise the potentially harmful effect of non-metallic inclusions, researchers and steelmakers continue to examine various characterisation techniques for non-metallic inclusions studies. The general expectations for characterisation techniques used for non-metallic inclusion studies are that it is relatively fast, involve less sample preparation, non-destructive and produce accurate or reliable analysis results, and Raman spectroscopy has these features.
The thesis used Raman spectroscopy to characterise synthetic non-metallic inclusions mostly associated with aluminium-killed calcium treated steels. The non-metallic inclusions used for this study were magnesium aluminate spinel MgO.Al2O3, calcium sulphide CaS and calcium aluminate phases (monocalcium aluminate CaO∙Al2O3, tricalcium aluminate 3CaO∙Al2O3 and mayenite or dodeca-calcium hepta-aluminate 12CaO.7Al2O3). The study demonstrated that the Raman spectra measured from the sample mixtures could provide qualitative and quantitative information for estimating the specific components in the samples. Additionally, this study investigated the prospect of using Raman spectroscopy as a characterisation technique for inclusion evolution studies and to predict the liquidus region within a CaO–Al2O3 binary system under steelmaking temperatures. The experimental measurements performed with Raman spectroscopy demonstrated to have a relatively short duration for sample preparation, fast results and can distinguish the synthetic inclusion phases based on their characteristic Raman bands features.
The study shows the use of Raman spectroscopy presents as a potential tool for steel cleanliness assessment through the identification and characterisation of non-metallic inclusions. Additionally, the study contributes towards the general need to have a more robust characterisation technique for non-metallic inclusion studies considering the contribution of steel cleanliness to the competitiveness and sustainability of the steel industry.