In Situ Observation of Precipitation Behavior of MnS during Solidification of Steel Melt Intended for Production of Nonquenched and Tempered Steel

Two heats of steel are melted using a vacuum induction furnace in the laboratory, with one heat undergoing magnesium treatment and the other being subjected to a combined magnesium-calcium treatment. The precipitation and agglomeration behaviors of inclusions of these two steel samples are observed using a high-temperature confocal laser scanning microscopy. MnS precipitates form around oxide cores and undergo rapid growth during the solidification process of molten steel, and these MnS precipitates with oxide cores react with the cores, resulting in the transformation of the MnS into complex sulfides. In comparison with Al2O3 inclusions, MgO<middle dot>Al2O3 inclusions have a lower critical velocity (V c), making them more susceptible to being engulfed by the solid-liquid interface. As the size of colliding inclusions increases, the coalescence-collision frequency (E 0) initially decreases until it reaches a minimum value. After that, with further size increments, the frequency starts to increase. During the inclusions growth process through collision, there is a distinct zone where coalescence-collision frequency is low. Inclusions that reach this zone struggle to grow further due to reduced collision coalescence, consequently leading to a predominance of inclusions with diameters in this zone. This article investigates the formation and collision behavior of inclusions in steels treated with Mg and Ca-Mg-Ca composite treatment. The study includes calculations of the critical velocity and coalescence-collision frequency of the inclusions. MgO<middle dot>Al2O3 have a lower critical velocity compared to Al2O3. Additionally, a distinct zone with a low coalescence-collision frequency is observed. image (c) 2024 WILEY-VCH GmbH