Database Clustering after Automatic Feature Analysis of Nonmetallic Inclusions in Steel

Abstract

Non-metallic inclusions (NMIs) in steel have a negative impact on the properties of steel, so the problem of producing clean steels is actual. The existing metallographic methods for evaluating and analyzing nonmetallic inclusions make it possible to determine the composition and type of NMIs, but do not determine their real composition. The analysis of single NMIs using scanning electron microscope (SEM), fractional gas analysis (FGA), or electrolytic extraction (EE) of NMIs is too complicated. Therefore, in this work, a technique based on the automatic feature analysis (AFA) of a large number of particles by SEM was used. This method allows to obtain statistically reliable information about the amount, composition, and size of NMIs. To analyze the obtained databases of compositions and sizes of NMIs, clustering was carried out by the hierarchical method by constructing tree diagrams, as well as by the k-means method. This made it possible to identify the groups of NMIs of similar chemical composition (clusters) in the steel and to compare them with specific stages of the steelmaking process. Using this method, samples of steels produced at different steel plants and using different technologies were studied. The analysis of the features of melting of each steel is carried out and the features of the formation of NMIs in each considered case are revealed. It is shown that in all the studied samples of different steels, produced at different steel plants, similar clusters of NMIs were found. Due to this, the proposed method can become the basis for creating a modern universal classification of NMIs, which adequately describes the current state of steelmaking.

Control of the Composition and Morphology of Non-Metallic Inclusions in Superduplex Stainless Steel

“…Along with the formation of pure stoichiometric inclusions, thermodynamic modeling considered the formation of complex inclusions in solid solutions. These are the particles most often found in steel [38]. Due to the release of excess free energy during the dissolution of inclusion components, the formation of NMIs solutions is energetically more favorable and provides lower concentrations of dissolved oxygen in steel.…”

Development of a Methodology for the Quality Management of Duplex Stainless Steels

“…Equations (1)–(3) consider only the elements that have a positive effect on the resistance to pitting corrosion, but they do not consider the harmful impurities of sulfur and oxygen [ 6 ], which form non-metallic inclusions (NMIs) that reduce the corrosion resistance of steels [ 20 , 21 , 22 , 23 ]. The distribution, quantity, size, and composition of NMIs depend on the technology of steel melting and deoxidation [ 24 ], and affect the corrosion resistance [ 25 ]. For example, pitting often occurs at the interface between inclusions and the metal matrix [ 25 , 26 ].…”

Classification of Hot-Rolled Plates Using the Mahalanobis Distance of NMIs in Ti-Stabilized Austenitic Stainless-Steel Produced by Secondary Metallurgy

“…In modern steelmaking, the formation, characterization and control of nonmetallic inclusions are becoming increasingly important, and tailoring inclusions to improve the properties and performance of steels, known as inclusions engineering, is indispensable [13][14][15][16][17][18]. When cleaner steel is required, additional analysis methodologies and techniques are demanded.…”

“…Automated inclusion analyses are able to overcome several weaknesses of traditional measures [14]. Therefore, a combination of techniques is recommended [16][17][18].…”

“…In the relevant scientific literature, NMIs are classified according to their type (carbides, nitrides, sulphides, oxides, etc. ), and other, more complex inclusion types is a well-covered topic [6,7,[9][10][11][13][14][15][16][17][18]. However, the use of NMI features for the detection of production abnormalities in terms of two-class classification has not been reported.…”