Chemical characterisation of non-metallic inclusions during casting of hot work die steel

Abstract

A chemical characterisation of the non-metallic inclusions in the aluminium killed tool steels during the casting process has been performed. The steel samples taken during the mould fillings, after casting and from the final products have been studied. The chemical compositions of the different phases in the inclusions have been analysed using SEM/EDX. Three types of inclusions, namely, type 6 (spinel surrounded by the calcium–aluminate oxide solution), type 7 (calcium–aluminate oxide solution) and type 9 (alumina based inclusions) have been found in the steel samples during the mould filling. Type 9 inclusions originate from the erosion of the nozzles and the closing gates during the mould fillings. The steel samples after casting contain four types of inclusions namely, types 6, 7, 9, 10 (alumina–silicate oxide solution) and 11 (spinel phase with calcium sulphide). The types of inclusions vary with the position in the ingot. In the steel samples from the final products three types of inclusions were detected, namely types 6, 7 and 11. The investigation have revealed that the increase in the sulphur activity of the steel melt during the casting is the cause of the formation of oxide sulphide and calcium sulphide phases in the inclusions detected after casting and in the final products.