Three-dimensional morphology and thermodynamic calculation of inclusions in stainless steel

The typical inclusions in stainless steels were extracted by the anhydrous electrolysis method, the three-dimensional morphology of the inclusions was observed by scanning electron microscopy (SEM), the inclusions were classified and analyzed according to the element composition, and the inclusions with the same chemical composition but different three-dimensional morphology were characterized and summarized. The equilibrium states of the different inclusions were calculated by the thermodynamic software FactSage 7.0, the effects of temperature and molten steel composition on the equilibrium states of inclusions were studied, and the corresponding equilibrium phase diagrams were obtained. In the results, the inclusions in stainless steels can be extracted effectively by the anhydrous electrolysis method, avoiding the error caused by the metallographic method, and the three-dimensional morphology of inclusions can be observed more clearly; according to the SEM observation and measurement, the enrichment area of titanium is likely present at the larger alumina inclusion surface, and most of inclusions are spherical and polyhedral with smooth surface, whose diameters are generally no more than 5 μm. According to the thermodynamic calculation, the inclusions in steels are closely related to the mass fraction of elements in steels; the different mass fractions of Mg, Ti, and Si elements may lead to the different inclusions at 1873 K.