Comparison of 2D and 3D morphology of non-metallic inclusions in steel using different methods

In the current work, the two-dimensional (2D) morphology of MnS inclusions with different shapes, including spherical, rod-like, flower-like, polyhedron and aggregated cluster, as well as spherical oxides were observed. The three-dimensional (3D) morphology of inclusions extracted from steel using acid dissolution, but the MnS was reacted away with acid during the extraction of the inclusion from the steel matrix. It is shown that the 2D method is hardly accurate to detect the morphology and size of inclusions comparison 3D morphology of inclusions. Therefore, a method of separation, extraction and analysis of non-metallic inclusions in steel was presented. Electrolytic extraction using non-aqueous electrolytes were performed to dissolve the conductive steel matrix and remain nondestructive inclusions. Scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS) was used to obtain the integrated 3D morphology, size and chemical composition of inclusions. The morphology of MnS inclusions was reclassified on the basis of the integrated 3D morphology under the following categories: elliptical, spherical, rod-like, plate-like, irregular or polyhedron, dendrite and patch MnS precipitated on the surface of oxides. Non-aqueous electrolysis extraction with the advantage of nondestructive to inclusions, low cost, and high efficiency, and the subsequent analysis of morphology, size and chemical composition is more reliable and accurate than the traditional method. What is more, it allows a better understanding of the origin and formation of inclusions, which is helpful for the control and removed of inclusions in steels.