Study on Inclusions Distribution Across the Thickness of Enameled Steel Slabs

Abstract

Enameled steel is widely used owing to its superior fatigue and strength properties. However, the presence of inclusions formed during the steelmaking process significantly affects these properties. Therefore, this study investigated a factory-enameled steel slab to elucidate its behavior. Additionally, the study analyzed the distribution of inclusions across the slab thickness, and characterized the variation in oxygen, nitrogen, carbon, manganese and sulfur contents. Moreover, the type, number density, size, and morphology of inclusions were examined across the slab thickness. The findings revealed that the center of the slab exhibited the lowest sulfur and manganese contents, which gradually increased toward the edges. Conversely, nitrogen content reached the maximum at the slab center and decreased toward the edges. The oxide inclusions mainly comprised Al₂O₃–MgO cores. Furthermore, the oxide inclusions in the slab mainly exhibited ellipsoidal morphology, with sizes concentrated between 1 and 5 μm. Moreover, the slab contained MnS and TiN inclusions, which exhibited symmetric variations in number density and average size from the edge to the center of the slab. The number density of MnS first decreased and then increased from the inner arc to the outer arc, while TiN exhibited the opposite trend. Additionally, MnS had a smaller average size than TiN, despite its higher number of inclusions. Furthermore, Ti₄C₂S₂ inclusions were mainly distributed between 1 and 3 μm and clustered in the slab. Additionally, theoretical calculations revealed that the elemental segregation trend followed the order of S > Ti > N > Mn. The sequence of precipitation formation was Ti₄C₂S₂ > TiN > MnS. This indicated a negative correlation between the cooling rate and inclusion size. Particularly, MnS exhibited the smallest size, while TiN featured the largest size at the center of the slab.