Thixomet Ltd., St. Petersburg, Russia

A. A. Kazakov, Dr. Eng., Prof., Head of the Laboratory of Metallurgical Expertise, e-mail: kazakov@thixomet.ru
D. V. Kiselev, Technical Director

Vyksa Metallurgical Plant, Vyksa, Russia

E. S. Mursenkov, Chief Specialist of the Engineering and Technology Center
V. A. Murysev, Chief Specialist of the Engineering and Technology Center

It is shown how thermodynamic simulation and the diagrams of phase equilibria of primary nonmetallic inclusions (NMIs) in steel obtained on its basis can be used for the interpretation of the nature and classification of the compositions of all NMIs formed in low-carbon steels during their treatment with calcium and cerium. Experimental data on the composition of inclusions obtained by SEM-EDS method are stored in the factory metallographic reports, prepared and analyzed by the Thixomet image analyzer, which is the key application for the metal products quality system. It is revealed that all endigenous inclusions are either products of steel overmodification with calcium (solid CaO and CaS with liquid calcium aluminates (CA) in various combinations), or undermodified magnesia spinel MgAl₂O₄ formed during magnesium reduction from deoxidized slag in the steel ladle. Exo-endigenous inclusions consist either of overmodification products sorbed on MgO-containing refractories and removed from their surface after deep infiltration together with MgO particles, or of undermodification products (CA + MgAl₂O₄) sorbed on the surface of ZrO₂-containing refractories without infiltration, but with partial dissolution of ZrO₂ in liquid calcium aluminates. The ratings of occurrence of certain combinations of phases in NMIs have been established and the details of their formation nature have been discussed to improve the metallurgical quality of steels by improving the ladle technology and casting.

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