and E. S. Borisovskii 621. 746.329 In Izhorsk Plant Production Union a furnace-ladle type unit for vacuum treatment and refining of steel is in service. In it electric-arc heating of the metal, electromagnetic stirring, vacuum treatment and desulfurizing of the metal, purging with oxygen and argon, and the addition of alloying additions are possible making it possible to obtain metal with the specified properties.The service conditions of refractories in such units are significantly more severe than in units of batch and circulating types [i, 2].The life of the best domestic periclase--chromite refractories in the lining of the slag zone of the vacuum ladle of the unit is only three to five heats and determines the life of the whole lining [3].Foreign experience shows that high-purity magnesia refractories from sintered and fused materials serve most successfully under such conditions [4].Since the basic carrier of limited silica in refractories is natural chromite added to increase heat resistance, tests were first set up to obtain a synthesized material which would contain the minimum quantity of silicon and calcium oxides and at the same time the chromite would increase the heat resistance of the material.The KhGSh spinelide was synthesized by fusion and sintering of mixtures of different original materials.Periclase, oxides, and spinel materials of high purity were used for synthesis of spinelide.In fusion into a block in an OKB-955N electric-arc furnace of mixtures of these materials, fused spinelide KhGSh-I through KhGSh-3 with a comparatively low content of silica and a high Cr203/Fe203 ratio was obtained (Table i)~ The mixtures were melted using a method making it possible to obtain high-quality KhGSh spinelide without ferrochrome.Alumina in a quantity of 200-400 kg per 1 m 2 of ~ea of decomposition of the electrodes was used as the base for the coke triangle, and the melting was done with a height of the layer of charged raw material mixture above the decomposition of 140-190 mm. The furnace was started up on Step I of the transformer and melting was done on step V. The melting time was 20-25 h.

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The effect of iron oxides on the structure and the properties of periclase-chromite refractories has been studied extensively [1][2][3][4][5][6][7][8][9].It was established that iron oxides participate actively in the diffusional processes of oxide redistribution between the main crystalline phases (periclase and chrome-alumina spinellide) of these refractories owing to the ability to change the valency from +2 up to +3 and to occupy the tetrahedral as well as the octahedral positions in the lattice of the spinels.This paper deals with a study of the capacity of certain other elements of variable valency to participate in the diffusional processes.We selected three elements of variable valency (titanium, manganese, and vanadium) that can form (just as iron) ions having a valency of +2 and +3 and radii close to those of Fe~ + and Fe s+ ( Table I).The mineral formation processes occurring in the refractory materials with the participation of manganese oxides were studied by Babin et al. [ii]. However~ these oxides were introduced as additives into chromium spinellide (chrome spinellid) containing iron oxides. Thus, the combined effect of iron and manganese oxides was studied.In the present investigation, we synthesized iron-free chromium spinellide and introduced each of the experimental oxide additives separately.Using chemically pure raw materials, various spinellides were melted in a 'Kristall ~ induction furnace.Each spinel contained magnesium, chromium, and aluminum oxides and one of the aforementioned elements. Table 2 shows the chemical composition of the obtained fused spinellides, their microhardness, and the temperature corresponding to the beginning of melting.For the purpose of comparison, we melted two spinellides incorporating iron oxide (F-I and F-2).Microhardness was determined at a load of 1.96 N using a PMT-3 tester.The relative error in determining the microhardness amounted to • Table 2 gives the values representing the average microhardness of 10 grains in each case. Table 3 shows the content of the oxides of the experimental metals in the charge used for melting and the decrease in their content during the course of melting.In the F-I, T-l, M-I, and V-I spinellides, the ratio of magnesium oxide and the remaining oxides was maintained close to the stoichiometric ratio at which the entire quantity of magnesium oxide is expected to enter the spinel.In other spinellides, an excess quantity of magnesium oxide (with respect to the stoichiometric composition) was introduced.The phase composition of the specimens was determined on the basis of the optical properties of the constituent phases and their local qualitative chemical analysis (a 'Camebax' microanalyzer was used for this purpose).In the T-I, M-I, and V-I specimens, a spinellide having a complex composition forms the main phase.Local qualitative chemical analysis showed that manganese oxide is present in the spinellide of M-I and vanadium oxide is present in the spinellide of the V-I specimen.Titanium oxide does not virtually enter the compos...

The use of unfired magnesite--chromite refractories in the metal zone of ladles of the ASEA-SKF equipment instead of high-alumina grade MKO-72 products improves the desulfuration of the metal when we use out-of-furnace refining; it prevents a reduction in the basicity of the slag due to destruction of the lining. Furthermore, the cost of the unfired basic articles is lower than for high alumina, and their manufacture requires much less fuel and energy outlay.Publications [1, 2] give the results of testing unfired magnesite--chromite in ladles. The main problem in making these is to ensure the minimum change in volume and strength during heating. A magnesia-spinel compound with a magnesium sulfate bond meets this requirement.To determine the technical parameters for such refractories in laboratory conditions, tests were made on two batches (Nos. i and 2). The starting materials consisted of waste magnesite--chromite brick (12.0%* Cr203) produced by the Magnezit Factory, chromite (45~ Cr203), and electrocorundum (98% A12Q ). Boric acid was added to stabilize the properties of the refractories during low-temperature heat treatment [3], and sulfite lye (pot-still residues) to confer green strength after pressing. The compositions of the batches are shown in Table 1.The monofraction powders were made separately. The combined-grind mixture was obtained by mixing in a vibromill the constituents premilled to fractions --0.063 mm. The magnesium sulfate and boric acid were added to the combined-grind mixture.