Revealing the morphology evolution and distribution of manganese sulphide in the 38MnS6 steel during continuous casting

ABSTRACT In this paper, the characteristics of manganese sulphide in the continuous casting bloom of 38MnS6 steel were revealed. Manganese sulphide in low oxygen (w(O) = 7 ppm) bloom mainly exists in the form of pure manganese sulphide distributed along grain boundaries. The morphology changes from fine droplets/rods to dendrites with large size and the aspect ratio gradually increases. The thermodynamic calculation results show that manganese sulphide precipitates at the end of solidification (f s = 0.86), and its morphology is related to local supersaturation and extrusion of solid-phase boundary. The solid-phase first transforms from high-temperature ferrite to austenite, then austenite grows up, which compresses the liquid phase boundary enriched with Mn and S and finally forms a large amount of manganese sulphide at the grain boundary. Dendritic, angular and droplet/rod manganese sulphide have different growth processes. Different types of morphological growth processes of manganese sulphide are described by combining crystal growth mechanism and solidification process.