In-situ Observation of Precipitation and Growth of MnS Inclusions during Solidification of a High Sulfur Steel

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The effect of the cooling rate on the morphology, number density, and size distribution of MnS inclusions in a high sulfur steel was investigated. With the increase of the cooling rate from 15 K/min to 300 K/min, the number density of MnS inclusions ranged from 91 #/mm² to 192 #/mm², and the average size of MnS inclusions decreased from 7.4 μm to 5.3 μm. A coupled model was developed to predict the precipitation and growth of MnS inclusions. The precipitation temperature of MnS at different cooling rates was approximately 1823 K, which agreed well with experimental results. Through the high-temperature confocal scanning laser microscope, the precipitation process of MnS in a high sulfur steel during the solidification was observed. Inclusions of MnS primarily precipitated at grain boundaries, while the morphology of MnS before and after solidification was influenced by the cooling rate. A higher cooling rate promoted elongated MnS inclusions precipitated, and smaller MnS particles were precipitated after solidification. Conversely, a slower cooling rate led to the massive MnS inclusions precipitated during solidification, leading to the formation of elongated MnS particles.