Extraction, Thermodynamic Analysis, and Precipitation Mechanism of MnS-TiN Complex Inclusions in Low-Sulfur Steels

Inclusions in square billets of low-sulfur steels employed in the production of steel springs were fully extracted using an improved non-aqueous solution electrolytic method and were characterized as oxides, MnS, and TiN-MnS complex inclusions. Inclusions were analyzed using SEM for their three-dimensional morphology. The formation mechanism of the complex TiN-MnS was investigated analyzing the equilibrium precipitation conditions during cooling from the liquid through solidification and in the solid state. In this analysis, three microsegregation models were employed. It was found that titanium nitride precipitates first and then manganese sulfide. Electron backscattered diffraction is employed to explore the crystal orientation relationship between TiN and MnS in the complex inclusions, which provided additional elements to fully describe the mechanism of formation of the observed TiN-MnS complex inclusions.