卷 49, 编号 3 (2019)

A method is proposed for calculating the convective heat transfer when a single circular jet interacts with a plane surface. The differences between this method and those currently existing are noted. The energy-dynamic potential of a flux and the energy-dynamic power of a flux are introduced. These concepts may be used to determine the rate of convective heat transfer at the gas–solid boundary. The differences between the proposed concepts and the existing concepts of the heat-flux density and heat flux are noted. The fundamental difference between the heat-flux density q and the energy-dynamic potential q_e is as follows. The heat-flux density q for convective heat transfer is the heat transferred from a liquid to a solid surface (or conversely) in unit time through unit area of heat-transfer surface. Thus, q characterizes the rate of convective heat transfer at a phase boundary. By contrast, the energy-dynamic potential q_e characterizes a property of the flux as a source or carrier of heat. Specifically, q_e characterizes the unit power of the liquid flux. In calculating the heat transfer, the jet interacting with the surface may be divided into two parts: before interaction, a simple jet; after interaction, a fan-like flux. It is not entirely correct to calculate the convective heat transfer in jet heating on the basis of the Reynolds number calculated from the characteristics of the gas leaving the nozzle. Instead, characteristics of the fan-like flux must be used: specifically, the initial mean velocity U_fan of the fan-like flux; and the distance from the critical point of the jet (the point of intersection of the jet’s vertical axis and the surface) to the current radius downstream. To assess the change in the basic characteristics of the free jets with different distances from the nozzle outlet to the boundary surface, we present expressions for the expansion coefficient of the jet; the injection coefficient of the jet; the velocity coefficient for any cross section of the jet (including or excluding the nozzle’s outlet cross section); and the ratio of the Reynolds numbers. Our findings confirm the need to calculate the heat transfer on the basis of the characteristics of the fan-like flux.

Metallurgical wastes are used increasingly in alloy production. Given the great volume and age of the recovered material, the content of undesirable elements and nonmetallic inclusions in the batch tends to increase. That sharply impairs the structure and properties of the castings obtained. In turn, that is reflected in the polytherms of the melts’ physical properties and correspondingly the necessary smelting temperature and time for heat-resistant alloys. In the present work, the temperature dependence of the electrical resistivity, the kinematic viscosity, and the surface tension are studied for heat-resistant Ni–Nb–Cr–Mo melts. For EP902 alloy, the critical temperatures leading to irreversible changes that improve the state of the melt are established. The quantity of foundry wastes in the batch affects the temperature dependence of the melt’s physicochemical properties. With increase in the quantity of foundry wastes in smelting, the critical temperatures rise. The influence of the state of the melt on the solidification and structure of the hard metal is investigated. Solidification of EP902 alloy is studied by differential thermal analysis. It is found that solidification begins with the deposition of a solid solution based on γ phase and ends with the formation of a eutectic based on the intermetallide Ni₃Nb. If the melt is heated above the critical temperatures, greater supercooling is observed but the eutectic temperature is practically unaffected. On the basis of the results for the melt’s physicochemical properties and its solidification, we propose high-temperature treatment of the melt to significantly improve the quality of castings obtained from heat-resistant alloys of EP902 type with a considerable content of foundry wastes in the batch. Experimental melts are subjected to mechanical tests with optimal high-temperature treatment of the melt. For melts containing 50% foundry waste, high-temperature treatment of the melt permits the production of castings with strength and plasticity that exceed the technical specifications and are consistent from melt to melt.

Controlled rolling may facilitate the transition from ferrite–pearlite structure to bainite structure and hence improve the strength of low-carbon alloy steel. A literature review shows the lack of detailed research regarding the type of bainite structure that ensures optimal properties of low-carbon alloy steel. To determine the temperature, time, and other parameters of treatment to produce such structure, it is expedient to establish the influence of the cooling rate on the structure and properties of low-carbon alloy steel. In the present work, we investigate the decomposition of supercooled austenite in low-carbon alloy pipe steel with 0.062% C, 1.80% Mn, 0.120% Mo, 0.032% Cr, 0.90% Ni, and other elements (Al, Cu, V, Nb, Ti). The treatment conditions producing bainite structure with elevated steel are determined for such steel. At low cooling rates (no more than 6°C/s), not only ferrite is formed in the microstructure but also granular (or globular) bainite consisting of bainitic α phase and an insular martensite–austenite component (1–6 μm). At a rate of 6°C/s, transition to rack bainite is observed; around the boundaries of the racks, carbides and residual austenite are seen. At cooling rates above 16°C/s, the bainite has packet–rack structure, Between 50 and 150°C/s, the mean rack width of the bainitic α phase declines from 2.24 to 1.32 μm.

A model system for decision-making support (a model of the blast-furnace process developed at Yeltsin Ural Federal University and PAO MMK) is considered. The basic model modules permit calculation of the material and thermal balances, simulation of the thermal, slag, and gas-dynamic conditions in the blast furnace, and selection of the batch composition. The model system, embodied as software, is integrated into the PAO MMK information system. The model for calculating the material and thermal balances permits determination of the Fe, S, Mn, and Ti balances. Introduction of the Slag Conditions software permits identification of the most important slag property to ensure normal slag conditions; determination of the ratio of the iron-ore materials so that the slag has the best viscosity and viscosity gradient; and the production of hot metal of the required quality. The introduction of Blast-Furnace Gas Dynamics software permits calculation and visual mapping of the gas-dynamic characteristics of the batch bed and assessment of the change in pressure difference and equilibration of the batch within individual zones of the furnace in the design period, with variation in the batch parameters and properties. The results obtained in practical use of this system are outlined. Recommendations are made regarding the solution of industrial problems.

Production technology is developed for capillary pipe used in disposable medical syringes. The heat treatment of the pipe in pure hydrogen with inert-gas injection is described. In industrial research, the annealing of the capillary pipe in an electrical furnace is optimized. The temperature field within the muffle furnace is analyzed. The optimal flow rate of protective gas and the limiting permissible flow rate of the injected gas (nitrogen and argon) are determined. The mechanical properties of the pipes (blanks) welded at Tyumen Medical-Supply Plant and manufactured at Pervouralsk New Pipe Plant (PNTZ) are studied. When using nitrogen as the protective gas instead of hydrogen, the likelihood of obtaining clean pipe surfaces is greatly increased.

The structure of high-strength 09Kh16N4BL and 14Kh17N2L stainless steels produced by casting on fusible models is studied. The influence of the steel composition on the content of nonmetallic inclusions in the cast steel is of considerable interest. The morphology of the nonmetallic inclusions is studied, and they are identified. Fractographic analysis shows that the nonmetallic inclusions affect the failure of the stainless steels. Two methods are used for quantitative assessment of that influence. Besides the classical methods, multifractal parameterization of the structure is employed to study the structure of the stainless steels. On that basis, correlations are established between the main multifractal parameters and the mechanical properties of the steel.

Analysis of two-stage iron and steel production by means of a blast furnace and an oxygen converter reveals its advantages and disadvantages. The main disadvantage is that carburization and decarburization of the metal are opposing processes and generate large quantities of waste with relatively high iron content. The organization of reduction and smelting of such waste—for the example of converter sludge—shows that direct reduction of iron by solid carbon, without carburization, is possible. Ore–coal pellets are produced experimentally. Their subsequent reduction and smelting yields metal ingots with the composition of steel.