Corundum-carbon refractories and ramming bodies are being used for lining cupola furnaces and mixer-type cast iron handling ladles [1][2][3][4][5]. Corundum-carbon refractories possess high slag resistance, but their apparent density and strength abruptly decrease with increasing carbon content. Furthermore, their low oxidation resistance forms one of the significant shortcomings.Additions of 5-15% silicon carbide and a mixture of silicon and aluminum powders have been suggested [5][6][7][8] for strengthening corundum-carbon refractories and decreasing the degree of oxidation of carbon.This paper deals with a study of the optimum content of the graphite and silicon carbide additives in a mullite-corundum body produced incorporating a binder based on orthophosphoric acid; for this purpose, the simplex-grid method of experimental planning was used. The content of AI=O3 in the original body amounted to not less than 88% * and the P202 content was 2.5-3.0%. We used crystalline graphite (GOST 5279-74) containing approximately 98% particles having a minus 0.09-n~n size and the No. 12/6 grade silicon carbide (GOST 3647-80). We introduced 5-15% graphite and silicon carbide additives into the ramming body.Cubic specimens having an edge of 40 mm were compacted from the experimental systems at a pressure of 30 N/mm 2. After drying, the specimens were placed in a Kryptol charge and were fired at 1580~for 6 h using a reverberatory furnace. The ultimate compressive strength of the fired specimens was determined.The crucible method was used to determine the resistance of the bodies to the action of slag and molten cast iron. The chemical composition of the slag was as follows, %: SiO2 42.98; AI203 10.24; CaO 39.75; MgO 2.71; MnO 2.26; FeO 3.02; K20 0.28; and Na20 0.Ii. The carbon content in the cast iron sample (chip) was found to be 4.47%. Along with slag pellets and cast iron chips, the specimens were placed in a Kryptol charge and were fired at 1500~ for a period of 2 h. After cooling, the area attacked by molten cast iron or slag was determined on the transverse section of the specimens.The degree of oxidation was determined from the changes occurring in the weight of the experimental systems during the process of heat treating at 800~ for 4 h in air. The heattreatment temperature (800~ was chosen based on the published data [7] indicating that the oxidation rate of graphite abruptly increases in the 650-800~ range and that it remains almost constant at a temperature exceeding 800~Heat treatment of the samples (weighing 30 g) was carried out in corundum crucibles.The following factors were chosen as variables: X I -content of the mullite-corundum body based on a phosphate 5inder with a 70-90% region of determination (range of variation); X 2 -content of the graphite additive with a 5-15% region of determination; and X 3 -silicon carbide content with a 5-15% region of determination.The investigated functions included the ultimate compressive strength of the specimens fired at 1580~ (Ocm, N/mm2); the area attacked (corroded) ...
In the least changed and transition zones of the experimenta! 0arts share ~s ~wo )~ three times less silica than in these zones of the PKhS parts (Table 3). The thickness o~ the transition zone of the experimental parts is two or three times less than in the PKhs parts.In the transition zone the silicates are primarily localized in the pores in the fo~z~T: of inclusions and the direct bond between the periclase crystals is essentially preserved~ which provides increased strength of the zone at high temperature ( Fig. 5b)~ As the result of the insignificant secondary recrystallization of peric!ase in the grains of filler in the transition (Kr. f = 1.04) and working (Kr. f = 1.23) zones the high structural inhomogeneity (K d = 10.4-16.4) and microfracturing are preserved (Fig. 5e, Table 4), causing wear primarily by peeling of thin layers and to a lesser degree by spells and fusion.In the reaction crust of the experimental parts in long service full replacement of the periclase with reaction spinelide of complex composition occurs (Table 3).
CONCLUSIONSA production test was made in the roof of a 180-ton open hearth of periclase--chromite parts produced by the Magnesite Combine from electrofused periclase--chromiteoThe life of the roof of experimental parts was an average of two campaigns of 690 heats~ which is three times longer than the life of PKhS refractories produced by the Nizhnii Tagil Metallurgical Combine.The difference in the life of the two forms of refractories may be explained by features of their phase composition, structure, and failure mechanism.
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