Morphological Changes Of Elongated Mns Inclusions During Heat Treatment Process

The element sulphur is usually added to form MnS inclusions and improve the machinability of micro-alloyed steel. However, the MnS inclusions tend to elongate in rolling direction during hot working process and deteriorate the mechanical properties of steels. In this work, the effect of heat treatment on the morphological changes of elongated MnS inclusions was investigated. The research results show that the as-cast type II MnS inclusions tend to flattened and elongated morphology after rolled. The shape changes of the MnS inclusions during the heat treatment process is flat -> cylinderization -> ovulation -> spheroidization. The morphological changes leading to cylinderization, ovulation and spheroidization of the MnS inclusions are controlled by the potential gradient induced by the inherent curvature difference. The transformation modes of ovulation and spheroidization depend on the initial aspect ratio (Length to width, L/W). The transport mechanisms for cylinderization, ovulation and spheroidization of the MnS inclusions are all controlled by surface diffusion.