Том 60, № 4 (2019)

We consider various types of design of the refractory equipment for the chambers of tundish ladles of continuous casting machines (CCM). The improvement of the equipment guarantees the efficient formation of metal flows and creates conditions for the improvement of its quality. We estimate the serviceability of partitions and baffles existing for the tundish ladles of CCM: their strength, the absence of cavitation, and the condition according to which the velocity of steel on the metal – slag interface must be lower than the permissible velocity.

The analysis of a heat transfer mechanism in the bulk of carbon-carbon composite materials was performed. It was experimentally determined that a homogeneous thermal condition is established at a depth of up to twenty structural cells of the composite. A characteristic layered porosity structure of the material formed by crack-like pores was revealed, and the extent of reduction in thermal conductivity upon splitting the samples into parts was determined. It was found that the process of cooling of the hot reinforcement rod in the carbon substance of the composite is less dependent on the effective thermal conductivity in the direction transversal to a bundle of parallel fibers in a 1D-reinforcement rod, and more dependent on the contact thermal resistance along the boundaries of the crack-like pores filled with air having a thermal conductivity of about 0.3 W/(m·K).

A heating of a carbon-made product and thermophysical properties of a carbon material in the temperature range from 300 to 2,500 K were studied. A discrete-heterogeneous mechanism of heating the surface of a multi-dimensionally reinforced carbon-carbon composite material (CCCM) subject to accelerated heating was revealed. Based on the results of testing carbon materials in the temperature range from 300 to 3,000 K, a numerical stress analysis of the product was performed, in which the arising stress condition was considered to be resultant from constraining the deformation of the heated parts of the product by relatively cold fragments. The safety factor levels were found for different parts of the product. It was shown that an additional increase in thermal strength as part of the combined definition of thermal resistance of CCCM products is associated with high thermal conductivity of 1D-reinforced rods of material structure.

The article presents an analytical review of publications on oxide ceramic binders that are used to prepare porous silicon carbide materials. The most promising ceramic binders are determined and the properties of materials based on ceramic binder data are provided. Mechanisms of modifier action making it possible to reduce the heat treatment temperature by up to 100°C are considered.

Characteristics of domestic corundum insulation objects are given. The properties of corundum lightweight objects obtained from microporous calcined alumina are studied. It is shown that product physicochemical properties are no worse than traditional lightweight objects of corundum composition.

A sharp reduction in the ultimate shear stress in the range of 20 – 80°C is observed during preparation of specimens of a clay component without thinners that facilitates development of cracks and defects. Use of pyrophyllite in ceramic mixes during specimen preparation provides a gradual reduction in the ultimate shear stress P_m in the range of 20 – 80°C. It is shown that in order to improve specimen drying properties a pyrophyllite – clay – water composition is more homogeneous than a clay – water composition Analysis of specimen P_m under hot forming conditions shows that the relationship Pm = f(t) is not as important as the relationship P_m = f(W,t), where t is temperature, and W is humidity.

Technological conditions for preparing ceramics based on MoSi₂ hardened by SiC and ZrB₂ that have enhanced physicomechanical properties (relative density ≥99.1%, bending strength 480 MPa) were experimentally investigated. The developed composites could be recommended for the creation based on them of functional structural ceramics operating at elevated temperatures in an oxidizing environment.

The technology for synthesizing TiN, ZrN, and HfN involves combustion in air of mixtures of aluminum nanopowder (NPAl) and the corresponding dioxides and contradicts thermodynamic calculations. Nitrides should be oxidized in the presence of air and converted to the oxides. The synthesis of nitrides in air is a new direction in the technology of refractory nitrides. Nitrogen from air is used in the proposed technology. The synthesis occurs at atmospheric pressure with free access of air. Complicated equipment is not required. Energy consumption is minimal. The synthesis proceeds spontaneously (exo-effect) after initiation. Mixtures of NPAl and the dioxides are reduced to the metals (Ti, Zr, Hf) or suboxides during combustion in air. Subsequent nitriding proceeds if the oxygen chemical activity is diminished.

The paper presents an experimental study of the effect that preliminary synthesis by iodine transport of ceramic powders with a core-shell structure has on apparent density, open porosity, elastic modulus, and sound propagation velocity of corundum ceramics sintered at various temperatures.

The analysis of literature data on the technological principles of controlling the formation of non-metallic inclusions in carbon and low alloy steels to increase their corrosion resistance in aqueous media is carried out. The key technological parameters of steel treatment in the ladle are summarized that ensure not only low contamination of steel with non-metallic inclusions, but also the formation of non-metallic inclusions of favorable morphology.

We present the results of investigation of the regularities of sintering and properties of corundum ceramics based on alumina with admixtures of ultradispersed powder of Al₂O₃(Al₂O₃ UDP) synthesized by the electrochemical method. It is shown that, as the firting temperature and the concentration of Al₂O₃ UDP increases, we observe a regular elevation of the linear shrinkage, microhardness, and ultimate strength in bending of the ceramics (the maximum values attained at 1550°C are as follows: 27.8%, 17 GPa, and 340 MPa, respectively). The introduction of Al₂O₃ UDP makes it possible to get an apparent density of the ceramics equal to 3.87 g/cm³ even at 1550°C.