A. R. Nikolaev

Thermophysical properties of tar-bonded refractories

ConclusionsAn investigation was carried out of the thermal diffusivity of as-molded, heat-treated, and coked dolomite, magnesite and dolomite-magnesite tar-bonded refractories by the even-rate heating of flat specimens to 200–1600°C in an inert medium.The relation was determined between the thermal diffusivity and the heat-treatment conditions and composition of the specimens; it was established that the disturbance of the monotonic temperature dependence of the thermal diffusivity arises primarily from Ca(OH)2 dehydration; it was shown that the thermal diffusivity is a function not only of the temperature but also of the rate of heating.The thermal capacity was determined by a known method for 1000–1900°C and calculated from the additivity of the thermal capacity of coked tar-dolomite refractories. The determined and calculated values differed by not more than 5–10%.The thermal conductivity of tar-bonded refractories was determined from the data relating to the thermal diffusivity and thermal capacity and compared with published findings. Up to 1000–1400°C the results obtained in this investigation lie within the spread of the published data.

Thermal diffusivity of resin-bonded refractories over a wide temperature range

Results are shown of thermal diffusivity measurements made on resin-bonded refractories of various compositions and structures.

RATIONAL SELECTION OF THE REFRACTORIES FOR SLIDE GATE PLATES

During teeming in operation of the gate the temperature field changes, but for a long time the temperature gradient changes but exceeds the limiting value. The greatest variations in temperature occur in the supporting portion in relation to the metal of the lower movable plate, which is responsible for reliable shutting off of the stream. The more shut-offs during teeming, the more intense the thermal action of the molten metal on the contact layer of the refractory. Corundum refractories are 1.5-2 times more heat resistant than periclase. Therefore, for gates for teeming on a continuous billet casting machine it is desirable to use periclase refractories, and in top teeming into molds corundum refractories. The essence of the corrosive action of molten steel on the gate plate material consists of spontaneous liberation on the contact surface of endogenic oxides of the primary oxide phase of the molten metal and subsequent development of the chemisorption process. The composition of the primary oxide phase is determined by the type of steel melted and the method of deoxidation of it. Depending upon the composition of the primary oxide phase the oxides precipitated may be in the liquid or solid state [2]. Steels containing flowable components of the primary oxide phase of the FeO-MnO-Si02 system, which are characteristic of rimmed and semikilled steels, are the most aggressive toward the refractory. Corundum refractories possess a lower resistance toward the corrosive action of such steels than periclase. Therefore, for teeming of them it is desirable to use periclase refractories. Since with an increase in temperature and contact time the corrosive action increases, for teeming on a continuous billet casting machine and teeming of large heats it is also desirable to use periclase refractories. Killed carbon steels are deoxidized with a somewhat larger quantity of silicon and sometimes aluminum is used. The oxide components of such molten steels are most frequently solid phases. In these cases there is not capillary penetration causing significant development of the depth of the reaction layer, and corrosion of the refractory is practically absent. In teeming of such steels the selection of the refractory is not signficant. Steels with an increased manganese content are distinguished by a significant quantity of its oxide in the primary oxide phase. In contrast to a periclase refractory, at the teeming temperatures a corundum refractory forms with this oxide a broad area of l~-melting compositions of secondary phases. Therefore in teeming of such steels it is desirable to use periclase refractory. An effective measure preventing penetration of the components of the primary oxide phase into the refractory is the introduction of carbon into the pores such as by impregnation by a coking hydrocarbon with subsequent heat treatment. It is desirable to use refractories with such a treatment for teeming of steels with fluid components of the primary oxide phase. Since corundum refractories are corroded more by these steels, treatment of them is more effective.

Relationship of the structure of slide valve periclase plates to their metal resistance

ConclusionsThe interaction of the original structure of periclase refractories, which is dependent upon their purity and structure, with the high temperature strength and metal resistance, was established. It was shown that samples of high purity fused periclase, in the structure of which coarse grains of fragmental structure predominate, had the highest resistance to the action of molten iron.

A laboratory study of metal-resistant sliding-gate tiles

ConclusionsThe feasibility of carrying out a laboratory study of the metal resistance of the refractory materials of sliding-gate tiles has been shown.Taking into account the user conditions of the gate tiles, we have developed a method for studying the metal-resistance of refractories under laboratory conditions. This method is based on the immersion of the specimens in molten steel.Criteria for a quantitative evaluation of the metal-resistance have been chosen; this makes it possible to forecast the behavior of the material during steel-casting.

Interaction of periclase and corundum refractories with iron and iron-manganese melts

ConclusionsThe authors have experimentally investigated the reaction of periclase and corundum refractories with iron and iron-manganese melts. They propose a physicochemical scheme of the reaction, taking account of the characteristics of the composition and structure of the specimens. They show the influence of manganese and of the composition of the primary oxide phase on the character of the reaction. The coefficients of diffusion of the primary oxide phase in periclase grains have been determined.

Standardization of the refractory products for the slide gates of steelcasting ladles

ConclusionsNew technical specifications, viz., TU 14-8-185-75 and TU 14-8-213-76, for the refractory products for the slide gates of steelcasting ladles have been prepared and put into effect.The standardization of the types, dimensions, and technical specifications of the refractory products for slide gates will help to improve the quality of the products and accelerate the changeover to an advanced method of steelcasting.