With the development of methods of processing steel outside the furnace there has been a change in the function of the ladle -from an intermediate container for transporting the metal it has been changed into a most important unit in which the steel is sequentially subjected to refining, blowing with inert gas, and vacuum treatment. Thus, the conditions of service for the refractory lining have been made much rigorous, since the dwell time of the metal in the ladle has increased from 20-30 min to 2-3 h, which has led to a reinforcement of the corrosive action of the steel and slag on the lining. Furthermore, there has been an increase in the abrasive action of the liquid steel on account of the more intense mixing during blowing and vacuum treatment [1][2][3].The use of chamotte linings in such conditions is undesirable, not only because of the sharp fall in the resistance of the ladle, but also as a result of its unfavorable influence on the purity of the metal [i, 2].For lining ladles used in processing steel outside the furnace more resistant high-alumina refractories are bing used [1][2][3][4], including those with additions of chromite [5].In Soviet and foreign practise there is experience with the use of unfired refractories of various compositions for lining ordinary steelcasting ladles [6][7][8][9].The unfired refractories compared with fired products possess a higher resistance to scaling under the action of liquid steel and slag, and low porosity, as a result of which they are less prone to penetration by metal and slag [8, 9].The present article presents the results of investigations into the development of a technology for unfired, mullite-corundum, and fired, mullite-siliceous refractories with additions of chromium ore, and also the results of comparative tests on experimental batches of the newly develope products and industrial mullite-corundum articles in the linings of steel ladles used in treating steel outside the furnace.The following material were used in the investigations: high-alumina chamotte containing 68% AI203 by weight, electrocorundum, Latnensk clay, and chrome ore. The chemical compositions of the starting materials are shown in Table i. Orthophosphoric acid was added to the bodies for the unfired products.The laboratory investigations established the optimum content of orthophosphoric acid in the bodies, e,~uring the production of high-quality green bricks and products, and these results also established the heat process schedule for the unfired and fired refractories.On the basis of the studies at the Semiluksk refractories factory we prepared trial batches of unfired mullite-corundum articles in amounts of about 220 tonnes and fired mullitesiliceous articles with additions of chrome ore in amounts of 50 tonnes.The articles were pressed on SM-I085 toggle presses with a moisture content in the body of 4-4.5%; the apparent density of the green brick for the unfired mullite-corundum articles was on average 2.73, and for fired brick containing chrome ore 2.90 g/cm 3.
Rigid demands are placed on refractories intended for design elements in steel ladles, especially in terms of density, strength, slag and metal resistance, and thermal-shock resistance.Periclase refractories are distinguished by a high resistance to the chemical action of molten steel and slag, but they have low thermal-shock resistance and mechanical strength and a high porosity. This paper gives the results of a study into the influence of compositional additions of Cr20a and Ti02 on the physical-ceramic and thermomechanical properties of specimens based on electrofused periclase with the aim of using the newly developed material in plant working at high temperatures and under melt conditions and thermal stress.The starting materials consisted of electrofused periclase of the following chemical composition, %:~ MgO 94.66, SiO2 1.88, AI20a 0.60, Fe20a 0.39, CaO 2.44, Am 0.44; chromium oxide OKhM grade as specified by GOST 2912-79; and titanium dioxide of chemical purity grade as specified by TU 6-09-2166-77.Specimens were pressed at 150 MPa from batches of the following grain-size composition: 45% electrofused periclase fractions 2-0.5 mm, 20% fractions 0.5-0.063 mm, and 35% fractions minus 0.063 mm. The compositional additives were incorporated in the finely milled form (minus 0.063 mm) as a result of reducing the amount of finely grained constituent of the batch.The bond consisted of an aqueous solution of sulfite lye with a density of 1.16 g/cm 3. The firing temperature of the perlclase specimens containing the additives was 1780~ with a soak at this temperature of 6 h.The results of the study of the effect of the additives on the main properties of the specimens are shown in Table i.The introduction of the compositional mixtures contributed to an increase in the apparent density of the fired specimens from 3.05 to 3.13-3.29 g/cm 3. A marked reduction in the open porosity (by about 4%) is noted only in specimens containing 5-10% Cr=Om and about 6.5% Ti02.Specimens containing more than 13.0% Cr2Oa, regardless of the content of TiO2, are badly sintered in practice.An increase in the open porosity in this case is possibly connected with the separation of chromium oxide from the system as a result of the oxidation of the chrome-spinel in the firing process according to the equation [i]:MgCr20~+l~502-~MgO+2Cr03.gas s~ g~ Uniformly with a reduction in the open porosity there is an increase in the mechanical strength to maximum values of 106 and 100.7 MPa, which correspond to specimens prepared from batches Nos. 8 and i0 (see Table i).The specimens' resistance to the thermal loading is in reverse relationship to the mechanical strength of the refractories.The highest thermal-shock values (3-4 heat cycles) are noted in specimens whose compressive strength is 28.2-66.3 MPa, which agrees with [2].The refractoriness under load of 0.2 MPa is reduced with increase in the content of titania, especially with a reduction in the amount of chromium oxide (batches Nos. 4, 5, and 7).The resistance of periclase specimens with the...
The mechanical properties of heterogeneous-composition refractories and polycrystalline ceramics at high temperatures vary considerably, both qualitatively and quantitatively. The deformation of polycrystalline aggregates is controlled by elementary diffusion-dislocation acts of cooperative or individual displacement of atoms in the volume and at the surface of crystallites [i]. The high-temperature plasticity of refractories made by the chamotte technology has a macroscopic character, and ensures mutual displacement of the structural elements due to the reduction in the viscosity of the bond mass [2, 3] (a similar deformation mechanism develops also in polycrystalline ceramics in the case of the formation of fusible interphase layers [4]). It is obvious that the strength properties of such materials, and in particular creep, are determined by the quantity, composition, and distribution of the bond, its structure, and the strength of binding with the chamotte grains.One of the main constituents of the bond in aluminosilicate refractories is the glass phase whose amount reaches 10-30% (parts by volume) depending on the type of refractory. It is precisely this fact, providing there is adequately uniform distribution of the glass phase, that causes a high plasticity in such refractories and their substantial densification during axial compression. Specimens of mullite-corundum refractory may be, for example, [5] deformed by about 20% without marked damage, and in this case their open porosity is reduced by 30% (rel.), and a deformation of about 50% facilitates a reduction in the porosity of 80% (rel.).Magnesia refractories, in contrast to aluminosilicate, do not contain glass phase. This contributes to the development of a large amount of direct bonds between the grains of periclase and chromite in periclase-spinel refractories [6,7] and hence extended sections of continuous crystalline framework. The bond part contains crystalline silicates, montichellite, merwinite, and forsterite with higher fusing temperatures than the softening temperatures of silicate glasses. These facts cause relatively weak deformation in magnesia refractories, and close to brittle destruction even at 1600~We carried out studies of the structural changes developing in high-temperature creep processes with monoaxial compression in magnesia refractories of several types.The objects of the study consisted of industrial articles produced by the Magnezit combine: periclase MO-91 (GOST 4689-76), periclase--chromite PKhP from fused powders , and periclase with a spinel bond PShG with the addition of alumina , and also experimental refractories made from fused periclase PP containing more than 95% MgO (mass parts) prepared at the Experimental factory of the Ukrainian Institute. For the creep measurements we cut out cylinders from the articles with diameter 36 and height 50 mm, and with axial apertures of 6 mm diameter. The axes of the specimens coincided with the direction of the pressing force of the articles. The properties of the specimens are s...
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