Physical and Technological Institute of Metals and Alloys (Kiev, Ukraine):

A. N. Smirnov, Dr. Eng., Prof.

Staryi Oskol Technological Institute named after A. A. Ugarov
(Staryi Oskol, Russia):
E. N. Smirnov, Dr. Eng., Prof., Chair of Metallurgy and Metal Science, e-mail: en_smirnov@i.ua
V. A. Sklyar, Cand. Eng., Associate Prof., Chair of Metallurgy and Metal Science

Ural Federal University (Ekaterinburg, Russia):
G. A. Orlov, Dr. Eng., Prof., Chair of Metal Forming

It is shown that when selecting the mould powder, it is necessary to take into account not only the standard (chemical composition, basicity, melting and deliquation temperature, viscosity in the operating temperature range), but also additional characteristics (physical state, the effect of non-wetting of the crystallizer surface with its droplets, initial solidification temperature), which have a very signifi cant effect on the formation of the billet. This will ensure optimal growth of hard crust, achieved due to the thickness of the mould powder layer. It is shown that the mould powder of well-known world manufacturers used for continuous casting of billets have low wetting parameters: the wetting angle of the liquid mould powder is ~154±2°. In the course of laboratory studies it was established that not all mould powders exhibit a characteristic «fracture» curve. The reason for this is that in these slags during solidification the crystalline phase is not released, i.e. the mould powder data form a vitreous phase during solidification. A rather simple experimental method for determining the degree of crystal state of slag-forming mixtures has been developed. The interrelation between the temperature of the beginning of solidification and the content of the crystalline phase in the mould powder slags for pouring a billet was established. In industrial conditions, the hypothesis of the need to take into account the totality of characteristics in the selection of the mould powder was confirmed. A study on the detection of subcortical blisters, which was performed by visual inspection of the surface of workpieces after face milling, showed that on the surface of the latter there are two types of bubbles due to low technological sophistication of the selected mould powder and obtained as a result of argon purging of the metal. It is shown that when steel is cast using a granulated mould powder, a sharp reduction in the number of manifestations of the subcortical bubble defect on the surface of the billet after it has been stripped is observed in comparison with the powdered mould powder of the current production. Comparison of casting data with argon purging and without purging showed that in the case of casting with argon, the number of detected bubbles is greater than in the absence of purging.

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