Том 46, № 8 (2016)

The thermal stresses in three types of iron-ore pellets with differentiated porosity are compared. The thermal stress of pellets obtained by the spraying of wet batch onto the batch coating and onto pelletized materials is analyzed. The influence of the porosity and thermal mass of the pellets on the thermal-stress distribution over the pellet cross section is determined. The variation in the strength of pellets with differentiated porosity over the cross section is assessed in the presence of a dynamic temperature field over the porous sphere. The role of the thermal mass in the core and shell of the pellet is also evaluated. The action of thermal stress in activating the sintering of iron-ore pellets is analyzed. Recommendations for improving the thermal conditions in pellet roasting are outlined. The best pore structure is obtained by forced nucleation of pellets, which results in elevated porosity in the core.

Since the mechanical properties of metals and alloys with ultrafine-grain structure are of great practical interest, the development of continuous methods of intense plastic deformation deserves attention. The introduction of nanostructuring methods in existing production processes is subject to numerous constraints, mainly associated with the dimensions of the machined workpiece. Continuous methods of intense plastic deformation must be introduced, with corresponding gains of expediency and productivity. The combination of different types of plastic deformation is promising. Carbon-steel wire is studied in the present work. If drawing is combined with external loading, its applicability in wire production may be greatly expanded. If drawing is combined with flexure and torsion, a new production technology may be developed for the production of ultrafine-grain components. In this approach, continuously moving wire is subjected to tensile deformation (by drawing), flexural deformation (on passing through a system of rollers), and torsional deformation. The instruments employed are versatile and compatible with existing industrial equipment. If drawing is combined with flexure and torsion, the carbon-steel wire produced are characterized by ultrafinegrain structure. This approach permits modification of the mechanical properties of the wire over a broad range, without loss of strength or plasticity.

The electrical resistivity of liquid nickel–chromium alloys is studied as a function of the temperature and concentration. Experimental data indicate that the dependence of the alloys’ electrical-resistance isotherms on the concentration is nonlinear. On the basis of the temperature and concentration dependence of the electrical resistivity of nickel and chromium alloys, the optimal conditions for the formation of microhomogeneous and equilibrium structure in the melt may be determined. The electrical-resistance isotherms of chromonickel alloys may be qualitatively explained on the basis of percolation theory and a quasi-chemical model of the microheterogeneous structure of molten metal alloys. The structure formation of chromonickel melts with increase in chromium concentration is characterized by the successive formation of clusters with different structure and dimensions.

The change in the structure–phase states and defect substructure of the rail surface after prolonged operation (passed tonnage of 500 and 1000 million t) is studied by optical microscopy, by scanning and transmission electron diffraction microscopy, and by measurement of the microhardness and tribological characteristics. It is found that the wear rate increases by a factor of 3.0 and 3.4 after passed tonnage of 500 and 1000 million t, respectively, while the frictional coefficient is reduced by a factor of 1.4 and 1.1, respectively. After 500 million t, the cementite plates break down completely, and rounded cementite particles (10–50 nm) are formed. After 1000 million t, the initial stage of dynamic recrystallization is noted. Possible explanations of the observations are discussed. Two competing processes may occur in rail operation: (1) fragmentation of the cementite particles, with their subsequent entrainment in the ferrite grains or plates (in the pearlite structure); (2) fragmentation and subsequent solution of the cementite particles, with transfer of the carbon particles to dislocations (Cottrell atmospheres) and transportation of carbon atoms by dislocations within the ferrite grains (or plates), culminating in the formation of cementite nanoparticles.

Statistical analysis of the chemical composition of high-temperature VZh159 nickel alloy in vacuum-induction melting and vacuum arc remelting yields regression equations that may be used to predict the metal composition in the ingots obtained by vacuum arc remelting as a function of the components in the consumable electrodes. The variation in oxygen, carbon, nitrogen, sulfur, and phosphorus concentrations in remelting is determined. The results are used in the design of production processes for high-temperature nickel-alloy ingots at PAO Ruspolimet.

Analysis of the literature on the thermophysical properties of mold flux shows that the measurement results for the thermophysical properties of the slag vary significantly, depending on the method employed. On that basis, a model is proposed for calculating the heat flux in the system consisting of the ingot, the slag film, and the mold. Literature data regarding the properties of the slag and industrial data regarding the mold’s wall temperature are employed here. The proposed model permits investigation of the heat flux as a function of the thickness and physicochemical properties of the mold flux.

A technology is developed for the production of highly alloyed (with up to 3% Si) isotropic electrical steel characterized by ultralow magnetic losses (P_1.5/50 ≤ 2.70 W/kg for strip of rated thickness 0.50 mm). The structure, texture, and magnetic and mechanical properties of vacuum-treated (<0.005% C) cold-rolled strip consisting of high-silicon steel (alloyed with >1% Al and >0.015% Sb) is investigated as a function of the heating rate and also the temperature and holding time in recrystallizing annealing. By refining the boundary conditions in the recrystallizing annealing of cold-rolled isotropic electrical steel, optimal grain size is obtained, and the pole densities of cubic orientations in the texture are increased. That reduces the magnetic losses.