Comparison of Three Approaches to Study Inclusions in Al-Si Deoxidized Steel and Al-killed Steel

摘要

Scanning electron microscopy with microanalysis by energy-dispersive spectrometry (SEM/EDS) can provide very useful information on the size, composition and prevalence of micro-inclusions. Reliable results require careful standardization of steel sampling and sample preparation for microscopy. In this work, the results from inclusion analysis were compared for three different methods of sample preparation: polishing of cross-sections, inclusion extraction by the bromine-methanol chemical method, and inclusion extraction by electrolytic etching (using a non-aqueous electrolyte). Examination of polished cross-sections has the important advantage that the process is readily automated, allowing hundreds of inclusions to be analyzed in a short time. Extracted inclusions reveal three-dimensional shapes (such as clustering) which are not apparent on two-dimensional cross-sections. A further concern is that sample preparation can cause contamination: For polished samples, care must be taken that no particles of the polishing medium (such as silicon carbide or alumina) remain embedded in the sample surface. During chemical or electrolytic extraction, the aim is to dissolve the steel matrix without attacking the inclusions, but the compositions of the inclusions themselves can be altered during extraction.1 For example, thebromine-methanol extraction method dissolves sulfide inclusions.2.