The factors responsible for the failure of blow plugs for steel ladles used in extra furnace steelmaking technology are considered. Results of a structural study of refractories based on electrofused corundum, crystalline silicon, and artificial graphite are reported. To improve the properties of corundum-carbon refractories, the sintering temperature should be increased to 1600°C.Blow plugs for steel ladles used in extra furnace steelmaking technology are fabricated from high-quality refractory materials. Under service conditions, the plugs are exposed to a number of factors that are capable of accelerating the wear of the plugs and finally lead to their failure. These factors are: inlet slit channels through which an inert gas is injected. The ingress of molten metal may cause irreparable damage to the blow facility;high temperature gradients and, consequently, high thermal stresses in the refractory material because of the cooling due to the injected gas; enhanced risk of erosion failure of the gas channel walls exposed to the gas jet and molten metal at the channel outlet in the steel ladle.In practice, blow facilities are subjected to a faster wear than nozzle blocks or ladle bottom lining and therefore require frequent replacement. Enhancing the service life of blow facilities is a challenging task; for its satisfactory solution, one will need innovative steps to be taken in both engineering design and advanced refractory materials. A step in this direction may be an adequate assessment of the physical, chemical, and mechanical properties of refractory materials potentially suitable for fabrication of blow facilities.
The effect of dopants graphite, boron carbide, and crystalline silicon on the physicomechanical and thermal properties of corundum-carbon refractories used in the fabrication of slot-nozzle tuyeres for off-furnace steel processing is discussed.Inert gas injection into molten metal ladle is currently becoming a trend in the off-furnace steel metallurgy. This technique involves processes essential for improving the metal quality: it makes the stirring of molten metal more effective owing to the gas bubbling; improves the homogeneity of the molten metal in temperature and chemical composition; reduces the concentration of undesired gaseous impurities; reduces the concentration of contaminants such as oxides and sulfur compounds, and facilitates dissolution and uniform distribution of deoxidizers, alloying agents, and slag-forming mixtures.A shortcoming of the gas injection technique is that it promotes corrosion of the ladle lining. The tuyeres through which an inert gas is supplied to the ladle become exposed to the most heavy-duty conditions [1] Apart from the main damaging factors -thermal and mechanical stresses, corrosive and erosive attack by stirred metal and slag, and bubble cavitation effect -other factors that specifically affect the performance of slot-nozzle injection tuyeres are added: thermal stress associated with the cooling and erosive action of the gas jet on the injection duct and the enhanced risk of molten metal ingress into the gas inlet system, frequently resulting in the duct clogging.To enhance the stability of slot-nozzle injection facilities (henceforth slot tuyeres for simplicity) against thermomechanical stress, and spalling and penetration of molten metal into the tuyere's slot nozzles, high-strength and thermoresistant refractory materials with minimum open porosity should be used.Promising materials for that purpose are corundum-carbon refractories [2]. Adding antioxidizing and structure-forming agents to the precursor mixture may provide the required physicomechanical, structural, and operational properties of the material [3].In this work we have studied the effect of additives (dopants) on the properties of corundum-carbon materials intended for the manufacture of slot-nozzle tuyeres for use in off-furnace steel treatment. The objects of study were laboratory specimens molded under pressure from fused corundum. The binding material was a phenolic powder (PP) and ethylene glycol (EG). The composites differed in structure-forming agents added. Composite 1 contained no dopant; composite 2 contained artificial graphite and boron carbide (B 4 C); composite 3 contained artificial graphite, boron carbide, and crystalline silicon.The dopants introduced into the refractory matrix produce a pronounced effect on physicomechanical properties and micro-and macrostructure of the material (Table 1; Figs. 1 -3). Corundum and corundum-carbon materials heat-treated at operating temperatures (1000 -1700°C) develop a range of sequential and parallel reactions that exert an individual effect on propert...
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