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.

A technique to assess microstructural anisotropy assessing by the thickness of the plate steel based on the texture analysis of the image has been developed. This technique provides for the anisotropy assessment at two dimensional levels: in the short-distance and long-distance neighborhoods, which characterize the elongation along the rolling direction of fine and coarse structural constituents, respectively. The practical approval results of this technique in the study of the microstructural heterogeneity of ferritic-bainitic steels over the thickness of 25-70 mm hot-rolled plates have been presented. It has been shown that the proposed anisotropy criteria in combination with the volume fraction of coarse packet-block regions of lath bainite as well as regions of bainite without an internal developed subgrain structure adequately estimate the microstructural heterogeneity over the thickness of plate steel and can be used for a detailed interpretation of the two-stage thermomechanical processing technology with accelerated cooling including taking into account the metallurgical inheritance of the slab.

Microstructural inhomogeneity comparative automated complex analysis of plate low-alloy cold-resistant steels for Arctic application with a thickness of 25, 50 and 70 mm, produced by thermomechanical processing technology with various temperaturedeformation parameters, has been performed. The inhomogeneity of the microstructure over the plates thickness was estimated by the volume fraction of coarse packet-block regions of lath bainite and regions of bainite that does not have a developed internal subgrain structure (conventionally called “non-granular” bainite), as well as anisotropy of the microstructure at different dimensional levels: short and long distance neighborhoods. The obtained results of microstructural heterogeneity quantitative assessment over the plates thickness were used for its detailed interpretation, taking into account the metallurgical inheritance of the slab and special features of two-stage thermomechanical processing with accelerated cooling.