Peter the Great St. Petersburg Polytechnic University (St. Petersburg, Russia):

A. A. Kazakov, Dr. Eng., Prof., e-mail: kazakov@thixomet.ru
A. I. Zhitenev, Engineer

The critical problems of nonmetallic inclusions in steel could be solved by interdisciplinary knowledge based upon steelmaking theory and practice, quantitative metallography and automated feature analysis based on the SEM-EDS analytical technique. A step-by-step method for interpreting the composition of NMI, determined by the SEM-EDS analytical methods, was developed and the nature of all NMIs has been interpreted using thermodynamic modelling. A technique for processing databases, obtained using an automatic feature analyzer (AFA), has been developed. Cluster analysis allowed generalizing these databases by combining NMIs into clusters according to the principle of similarity of their chemical composition and temperature-time nature, depending on the technology of deoxidation and modification of steel. The composition of inclusions along with a large number of analyzed particles, in combination with the methods of thermodynamic simulation makes it possible to restore the temperature-time nature of inclusions, taking into account the entire variety of associated processes occurring in liquid and solidifying steel. Comparison of the determined compositions of NMIs with the results of thermodynamic simulation makes it possible to establish the nature of each cluster of NMIs, associating it with one or another stage of the ladle treatment, casting or solidification. This information is necessary for the development of technological recommendations aimed at increasing the “cleanliness” of steel by NMIs. 

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