National University of Science and Technology “MISiS”, Moscow, Russia:

S. V. Podkur, Postgraduate Student, Dept. of Steel Metallurgy, New Production Technologies and Metal Protection
G. I. Kotelnikov, Cand. Eng., Associate Prof., Dept. of Steel Metallurgy, New Production Technologies and Metal Protection1, e-mail: gikotelnikov@yandex.ru
D. V. Karavaev, Postgraduate Student, Dept. of Steel Metallurgy, New Production Technologies and Metal Protection
S. A. Botnikov, Cand. Eng., Associate Prof., Dept. of Energy-Efficient and Resource-Saving Industrial Technologies

The level of sorting of steel at a metallurgical enterprise depends significantly on the content of carbon and hydrogen in the steel. The task of the work was to determine the optimal ratios of the concentrations of these elements, providing a minimum level of sorting of continuously cast billets and sheets. The increase in carbon and hydrogen in the steel of the tundish prevents the formation of nonmetallic inclusions, reduces the oxidizing ability of H₂O and reduces the sorting of steel by such defects as "captivity" and "bubble-swelling". It is shown that these defects are related to each other and are formed by the same chemical reactions of decomposition of water molecules by deoxidizing elements contained in the metal, such as Al, Si, Mn. In high-carbon steels, in order to reduce the number of "ultrasound defects", "network cracks" and breaks in the crust of a continuously cast billet, it is necessary to reduce the [H] content in the tundish metal. This is due to the fact that segregation processes develop during casting with the participation of dissolved carbon and hydrogen, followed by the release of H2 from sections of the steel supersaturated with hydrogen. It was found that in order to reduce the level of sorting at the enterprise and improve the quality of cast steel, it is necessary to ensure the optimal ratio of carbon and hydrogen in the metal at the tundish stage in accordance with the equation: [H, ppm] = -68.782 ∙ [% C] + 15.962. This equation is valid for low-alloy steels with a carbon content of 0.13 to 0.22%. For [C] < 0.13%, the recommended concentration of [H] is 7 ppm, and for [C] > 0.22%, the lowest possible hydrogen content in the steel should be.

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