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The peculiarities of the process of forming complex compounds, namely, spinels, in flux-cored arc welding for the slag TiO2-MnO-SiO2-MgO-CaO-FeO-Al2O3 system are studied. An experimental investigation of the mechanism of spinel formation in conditions of electrode arc welding and cladding under flux is carried out. Based on the analysis of microimages of the slag surface obtained using scanning electron microscopy, the mechanism of spinel formation, namely, the growth of microcomplex compounds into macrospinels, is presented. The main stages and mechanism of formation of the complex compounds, namely, spinels, are described. As shown, the structure of spinels is determined by the temperature conditions of the crystallization of the slag melt. The study reveals that one of the determining factors of high-temperature separation of the slag crust during multilayer cladding with overlap of the previous layer is the formation of spinels at the interphase boundary between the slag and the metal. Based on modern ideas about the structure of slag melts, a mechanism for the formation of complex compounds at the interphase boundary between slag and metal is proposed. The main factor determining the process of high-temperature separation of the slag coating for the TiO2-MnO-SiO2-MgO-CaO-FeO-Al2O3 system is the formation of complex compounds based on spinel-forming elements and slag oxides at the interphase boundary between the slag and the metal. [ABSTRACT FROM AUTHOR]

The blast furnace is the dominant high-temperature reactor in the modern ironmaking industry. Iron oxide in iron ores can be converted to metallic iron through blast furnace smelting, and this high-temperature melting can be used to separate the molten iron from the gangue components. The formation and thickness of the hot-surface slag crust on the copper stave in the high-temperature area of the middle and lower parts of the blast furnace are crucial for the safe operation and long campaign of the blast furnace. To enhance the precision of determining the thickness of the slag crust in this specific region, samples were extracted from the hot surface of the copper cooler situated in the high-temperature area. This extraction was carried out during the maintenance procedure of the blast furnace stockline. Subsequently, the thermal conductivity and melting performance of the slag crust were measured. The slag crust thicknesses corresponding to the various temperature measurement sites of the stave were determined by developing a mathematical model for the heat transfer of the copper stave. The actual slag crust thickness measurement data were acquired while the blast furnace stockline was in operation, and the data were then utilized to corroborate the model's predictions. A blast furnace with an effective volume of 3200 m3 was used to test the model. The average thickness of the hot-surface slag crust was computed for cases that occurred between 2020 and 2022. The data's correlations with the blast furnace's technical and economic indices during the same time period were examined. The findings indicated that the blast furnace's operation indices improved with a thinner slag crust, but there was also a higher chance of damage to the copper stave's internal cooling water pipes. Taking into account the technical and economic indices as well as a long campaign of the blast furnace, 150–200 mm is recommended as the appropriate average slag crust thickness on the surface of the copper stave in the high-temperature section. [ABSTRACT FROM AUTHOR]

The blast furnace is the dominant high-temperature reactor in the modern ironmaking industry. Iron oxide in iron ores can be converted to metallic iron through blast furnace smelting, and this high-temperature melting can be used to separate the molten iron from the gangue components. The formation and thickness of the hot-surface slag crust on the copper stave in the high-temperature area of the middle and lower parts of the blast furnace are crucial for the safe operation and long campaign of the blast furnace. To enhance the precision of determining the thickness of the slag crust in this specific region, samples were extracted from the hot surface of the copper cooler situated in the high-temperature area. This extraction was carried out during the maintenance procedure of the blast furnace stockline. Subsequently, the thermal conductivity and melting performance of the slag crust were measured. The slag crust thicknesses corresponding to the various temperature measurement sites of the stave were determined by developing a mathematical model for the heat transfer of the copper stave. The actual slag crust thickness measurement data were acquired while the blast furnace stockline was in operation, and the data were then utilized to corroborate the model’s predictions. A blast furnace with an effective volume of 3200 m3 was used to test the model. The average thickness of the hot-surface slag crust was computed for cases that occurred between 2020 and 2022. The data’s correlations with the blast furnace’s technical and economic indices during the same time period were examined. The findings indicated that the blast furnace’s operation indices improved with a thinner slag crust, but there was also a higher chance of damage to the copper stave’s internal cooling water pipes. Taking into account the technical and economic indices as well as a long campaign of the blast furnace, 150–200 mm is recommended as the appropriate average slag crust thickness on the surface of the copper stave in the high-temperature section.

The relevance of using slag crust separation methods, which are characterized by easy separation and are based on thermodeformation processes in the sample, is shown in the development of new welding materials. The developed method of assessing slag separation based on the theoretical calculation of thermo-deformation processes in the base metal has passed the stages of experimental research The experimental approbation of the proposed methodology for assessing the separation of the slag coating from the surface of welded joints under experimental fluxes based on the TiO2-MnO-SiO2–MgO–CaO-FeO-Al2O3 slag system was carried out for different welding regimes. The evaluation criterion for the high-temperature separation of the slag coating takes into account: the ratio of the geometric parameters of the test sample, the amount of heat input during the surfacing process, and the factor of the presence of spinelforming components at the slag-metal interface. The selected parameters for evaluating the separation of the slag crust in points, where the guaranteed separation of the slag coating is counted for the arbitrary separation of the slag during its destruction or the arbitrary separation of the slag by a monolithic layer. The practical value of the proposed method lies in the possibility of quantitative assessment of the probability of high-temperature separation of the slag coating for a wide range of fluxes for surfacing. The results of the conducted experiments show the efficiency of the developed methodology for evaluating the high-temperature separation of the slag coating from the surface of the weld metal. [ABSTRACT FROM AUTHOR]

Copper staves have been widely applied in large blast furnaces especially those whose inner volumes exceed 2000 m3 due to high cooling capacity. In the past decade, copper staves suffered severe damages in some blast furnaces, which not only shortened their campaign lives, but also caused huge economic losses. In order to make out this phenomenon, the damage mechanism of copper staves was investigated via analyzing the chemical composition, thermal conductivity, metallographic aspects and microstructure in this paper. As a result, the working state was more likely to damage copper staves instead of their materials. At the beginning, the poor quality of the coke and the large bosh angle promoted the development of edge airflow, which intensified the erosion of refractory materials, resulting in the fall-off of slag crusts and damage of cooling water pipes. After repair, the cooling capacity of copper staves still declined, causing the temperature to rise easily; consequently, hydrogen attack happened when the temperature reached 370 °C, which degraded the performance of copper staves. Therefore, copper staves were worn too quickly to form slag crusts, which finally failed under the hydrogen attack and the scouring of the edge airflow at high temperatures.

The composition of the ladle slag in units designed for the secondary treatment of steel needs to be optimized in order to increase the service life of the units' linings. On the one hand, the slag subjects the refractories to chemical wear. On the other hand, under certain conditions the slag is capable of forming a protective crust inside the units. The Nizhniy Tagil Metallurgical Combine has chosen certain refractories for the most heavily worn part of the lining of its vacuum chambers, since only the installation of a lining of a differentiated design that equalizes the rate of wear around the lining's perimeter will allow the desired effect to be obtained from optimizing the composition of the slag. An efficient composition for the slag was also chosen, the slag having high contents of MgO and AlO. The use of such a slag helps form a protective slag crust of the composition MgO·AlO on spinel refractories having the compositions MgO·CrO and MgO·AlO. [ABSTRACT FROM AUTHOR]

Copper staves have been widely applied in large blast furnaces especially those whose inner volumes exceed 2000 m3 due to high cooling capacity. In the past decade, copper staves suffered severe damages in some blast furnaces, which not only shortened their campaign lives, but also caused huge economic losses. In order to make out this phenomenon, the damage mechanism of copper staves was investigated via analyzing the chemical composition, thermal conductivity, metallographic aspects and microstructure in this paper. As a result, the working state was more likely to damage copper staves instead of their materials. At the beginning, the poor quality of the coke and the large bosh angle promoted the development of edge airflow, which intensified the erosion of refractory materials, resulting in the fall-off of slag crusts and damage of cooling water pipes. After repair, the cooling capacity of copper staves still declined, causing the temperature to rise easily; consequently, hydrogen attack happened when the temperature reached 370 °C, which degraded the performance of copper staves. Therefore, copper staves were worn too quickly to form slag crusts, which finally failed under the hydrogen attack and the scouring of the edge airflow at high temperatures. [ABSTRACT FROM AUTHOR]