Comparison of Methods for Analyzing Corrosion-Active Non-Metallic Inclusions in Steels

Keywords

steel, corrosion-active non-metallic inclusions, structure, dissolution, fracture, fractographic analysis

Abstract

A critical analysis of the literature regarding methodological approaches for analyzing the number and chemical composition of corrosion-active non-metallic inclusions (CANI) in metals has been carried out. The advantages and disadvantages of the metallographic method (ASTM E45), chemical and electrochemical dissolution of the matrix, and studies using SKPFM, SEM, or TEM microscopy are highlighted. Fracture surfaces of steels 20, 40Kh, U8, and 38KhN3MFA were obtained by tensile and impact testing; fractographic studies, and chemical and quantitative analyses of CANI were performed. It is shown that when inclusions are studied using the metallographic method, small-sized inclusions are not accounted for, and their chemical composition is distorted, as in the case of chemical and electrochemical approaches, since particles interact with processing media. During fractographic evaluation of CANI and their chemical composition, the analysis is carried out on an almost juvenile surface. EDX analysis of particles reflects their real chemical composition. Since cracks formed on the fracture surface propagate through stress concentrators (CANI), the fracture visualizes the maximum concentration of inclusions.

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