Non-metallic inclusions in the ingot and final products of a medium-carbon tool steel

The present work was carried out at Uddeholm Tooling AB, Sweden to study the inclusion characteristics in the ingot and the final product of a 'medium-carbon' tool steel. Steel samples were taken during the mould filling, after casting and from the final product. The inclusion populations in the steel samples were examined under a light optical microscope. The chemical compositions of the inclusions were analysed using a scanning electron microscope attached with EDX The steel samples taken during the mould filling were found to contain alumina-based inclusions, originated from the erosion of the closing gates, the inner nozzle and the outer nozzle. The analyses of the steel samples from the solidified ingot revealed a non-uniform distribution of inclusions. The inclusion population was found to be highest in the centre part of the ingot and lowest between the central line and the mould wall. The steel samples from the bars of the final products were taken at an identical position in each case, corresponding to the central part of the ingot. The inclusion populations were found to be somewhat higher in the final product in comparison with the populations before casting. The inclusion populations in the final products were also found to increase with the ladle age.