The resistance of magnesian spinellide refractories to molten slag attack is studied and effects associated with the material composition and the microstructure of test specimens are discussed. The mechanisms of corrosion wear and chemical reactions involved are considered in detail. Slags with a basicity of 1.9 -2.1 react with periclase to yield spinel, calcium orthosilicate, and monticellite. To prevent the chemical corrosion of periclase, sintered periclase or alumina as additions to the slag are recommended for use.
In efforts to reduce metal costs, it is important to extend the lining life in metallurgical systems [1]. In particular, the linings of vacuum units account for a considerable portion of total refractory costs.Three groups of factors affect the lining life in cir culatory vacuum units [2]:(1) structural factors (the shape and size of the metal framework, the lining design, the format of the refractory pieces, and so on);(2) the physicochemical properties of the refracto ries, which depend on the quality of the raw materials, the manufacturing technology, and so on; (3) technological factors (the operating conditions of the metallurgical system, the slag composition and properties).Specialists at OAO EVRAZ NTMK have been studying these factors, in order to improve the refrac tory components and optimize their operating condi tions. The results assist in the development and intro duction of new lining configurations with improved performance and longer life.On that basis, measures have been taken to improve the operation of the vacuum units at OAO EVRAZ NTMK. STRUCTURAL FACTORSIn the converter shop at OAO EVRAZ NTMK, the lining configuration illustrated in Fig. 1 is employed in the vacuum unit. A deficiency of this configuration is that the junction of the refractory ring and the refrac tory concrete at the end is rapidly worn, as is the region where the transporting gas is supplied (Fig. 2). During operation, the liquid steel penetrates into the damaged surface and erodes the metallic plate that supports the refractory rings at the end of the tube. That leads to settling of the lower ring of the tube and the formation of a gap between the rows of components. In subse quent operation, metal melt leaks into the gaps, pro ducing local erosion around the circumference (Fig. 3). The vacuum chamber requires premature repair [2,3]. This problem at the junction of the refractory concrete and the refractory rings may be eliminated by adopting the design in Fig. 4. In that case, there is no horizontal junction between the concrete and the refractory ring, and the lower ring is rigidly fixed. In the course of operation, the modified structure does not permit per ceptible settling of the refractory rings. The mean life in experimental vacuum chambers was 106.0 melts (as against 102.0 melts for mass produced components). PROPERTIES OF THE REFRACTORIESSpecialists at OAO EVRAZ NTMK pay great attention to the refractory components obtained from suppliers and, in particular, their susceptibility to wear [4]. Research shows that the unit wear of refractories in the discharge tube does not depend on the overall properties but is largely determined by the characteris tics of the intake refractories. The operating condi tions are most intense at the intakes: additional cool ing of the refractory surface in the period between melts by neutral gas and considerable turbulence of the metal, which tends to erode the brick.It is evident from the table that the components dif fer considerably in properties and working life. For more detaile...
Oxygen distribution is of great significance in the interaction processes of molten steel with oxide refractories. We shall examine two possible modes of oxygen migration in the oxide refractory--steel interface region at high temperatures which are tentatively designated as the physical and chemical modes.A gas phase is formed over the refractory due to the dissociation of the oxide according to the equation:*
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Results are provided for a study of the operating conditions of the refractory lining of steel-pouring ladles of OAO Nizhnetagil Metallurgical Combine, that are subject to the corrosive physicochemical action of slag and metal during steel smelting from vanadium-containing raw material. Manufacturing technology is proposed for corundum-periclase-carbon objects with improved quality indices, high resistance and reliability.Under conditions of the financial and economic crisis there has been a sharp increase in the importance of finding and introducing refractory materials that would be more rational with respect to the price:quality ratio. Within the structure of expenditure for refractories as previously the most expensive remain the linings of steel-pouring ladles. In fact, a considerable amount of work is carried out to reduce expenditure on this lining.In the recent past for lining steel-pouring ladles in the slag and metal areas peiclase-carbon refractory objects have been used, differing only in carbon content. Later, without changing the type of refractory, higher quality periclase has been used for the slag zone than for the metal area. However, periclase-carbon objects, that exhibit a number of valuable properties, had a specific plank with respect to life, since with the necessary replacement of individual lining elements with more than a single shutdown of the ladle, i.e. with profound cooling of the lining, considerable crack formation has been observed with escape in some cases of melting products through ladle equipment and casings.At almost the same time everywhere, i.e. abroad and within Russia, for further improvement of life, and consequently a reduction in expenditure, spinel refractories started to be used, of which preference was given to spinel-forming compositions that provide compaction of the lining during operation. Here lining life increased significantly, but the weaker areas remained the zone of metal stream impact, and also the zone subject to descending and ascending metal flows during metal treatment with argon. Action of the first, hottest portions of metal, the kinetic energy of the falling metal stream, and eddy flows, caused considerable refractory erosion.Production of steel in the converter workshop of OAO NTMK provides for steel smelting by both mono-and duplex-processes from vanadium-containing raw material, treatment of molten metal in furnace ladle devices and evacuation units, and continuous casting in CBCM. The metal is in the steel-melting ladle for 120 -240 min (depending on the steel grade and type of CBCM). In the converter slag under OAO NTMK conditions there is a considerable amount of RnOn-phase (Fe 2 , Mn 2 , Mg 2 )O. Vanadium is within the composition of vanadium calcium titanate and iron-vanadium spinelid. Both phases are solid solutions of complex composition. As a rule, vanadium is in the slag in a trivalent state. A further study of slag, taken directly from the wall lining of a ladle, showed presence of vanadium in the slag in a pentavalent state.The increa...
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