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Progress in the field of metallurgy has increased the demand for refractories and has demanded a constant improvement in their quality. Among the technical properties of refractories, one of the most important is slag-resistance, which characterizes the tendency of the refractory to resist the destructive effect of molten slags.Slag-resistance is evaluated from the loss in volume or mass of the refractory under the action of slag and from the depth of penetration of slag into the refractory.In recent years some studies have appeared in which the wear of a specimen in dynamic slag-resistance tests was estimated from the change in the chemical [I] or isotopic [2] composition of the melt or from the change in its physical properties, for example density [3]. Methods of determining the slag-resistance are constantly being reported and in these methods a larger and larger number of factors in the actual service of refractories, such as the gas medium, thermal shock, and large temperature gradients [4], act on the specimen to be tested. When reproducing the most important factors, there must always be a correlation between the results of the laboratory tests and the results in service.Equipment to determine the slag resistance at temperatures up to 1750~ has been developed at the All-Union Institute of Refractories.This equipment is based on a Tammantype high-temperature device made by the Experimental Workshop of the Urals Scientific Center of the Academy of Sciences of the USSR.The equipment includes: an electric furnace with a graphite heater with an internal diameter of 85 mm; a mechanism for inserting and removing the crucible; the insertion, removal, and rotation of the experimental specimen; systems for the electric supply, temperature measurement, cooling, inert-gas supply; and the automatic units.The layout of the equipment is shown in Fig. i.In the first adjustment period during furnace operation it was found that the working zone was insufficiently stable, its position depended on the quality of the assembly and it changed from one heating to the next.In order to increase the stability of the zone, heaters with a narrow throat in the middle, 115 mm long, 90 mm in external diameter, and with 96-98 mm diameter leads were used. This made it possible to have a stable working zone of a height of i00 mm and a temperature difference of < • and, for the same current and voltage, to reduce the warm-up time of the furnace.The furnace 1 was insulated with a charge of magnesite powder.The electric supply to the heater 2 is fed through the water-cooled leads 3 from the ac supply via the furnace transformer 4 whose primary winding is connected in series with the power unit and the thyristor voltage controller 5. The control makes it possible to change the voltage across the heater from 0 and 15 V. The system provides automatic control of the testing temperature using the Sh4501 contact millivoltmeter and the control unit (CU) of the thyristor voltage control.The maximum working voltage is established across the heater an...

It is known that the degree of wear of the refractory plates in the slide valves of sLeel teeming ladles is determined primarily by their service conditions.Plates of the same mroducing plant provide normal teeming in some steel plants but in others may not be used and require replacement by stronger ones.The structure of refractory plates may also influence their life.For example, a comparison of the character of the structure and high temperature strength characteristics of corundum plates with their service results showed the possibility of evaluating plate quality from these indices [i].It has also been established that depending on the form of the periclase grains, which is the basic index of their purity, plates differ significantly in high temperature strength and thermal resistance, which correlates well with the service results of periclase plates. An increase in impurity content, primarily silicates, leads to the formation of an unsatisfactory microstructure, with the formation of fine layers between the periclase grains, and to a reduction in the life of the periclase plates.Petrographic investigation of magnesia plates after service showed that a substantial role in their wear is played by the formation of lamination cracks as the result of a reduction in the high temperature strength of the material [3].The relationship of the high temperature strength and wear of periclase refractories in teeming of steel to the content and composition of impurities, which determine the degree of development of direct bonds in the structure, has been described in [4]. Obviously, a generalized investigation of the relationship between the metal resistance of refractories for slide valve plates and their structure has great significance in the search for means of increasing their life and reliability in service.The investigations were made on samples cut from pieces for an MSP-95 periclase plate and produced at refractory plants (samples No. 1-4) and in the institute (sample No. 5). The pieces (standard) for samples No. i, 2, and 4 were made from fused periclase with 96-98 wt.% MgO and the piece for sample No. 2 was taken during the period of introduction of a method, including addition to the charge of 0.5% B~O3.The piece (experimental) for sample No. 3 was prepared from burnedpericlase clinker.The refractory from uhich sample No. 5 was cut was a biceramic insert.Its working portion was made from special purity periclase with a weight percentage of MgO of more than 99% with a sintering addition.The characteristics of the investigated samples are presented in Table I.The microstructure of the samples* is shown in Fig. i. Samples No. 1 and 4 have a similar structure characterized by the presence of sharp-angled and single-crystalline aggregates of 0.2-1.5 mm periclase grains and fine rounded grains.The silicates (monticellite, dicalcium silicate) form 0.01-0.05-mm filaments between the periclase grains.The voids are quite uniform in shape (elongated) and size (width 0.03-0.06 mm). At the interface of the filler and the...