Vol 2019, No 7 (2019)

Abstract—The reducing roasting of hematite-type laterite nickel ores with flux CaCO₃ (limestone) and CaF₂ (fluorite) additions on a coal substrate in the temperature range 1350–1450°C, which causes the formation of granulated nickel-containing cast iron, is studied. The roasting time is 8–10 min without additional holding. The intense coalescence of metallic particles and the separation of metallic and slag phases is detected at 11–13% solid reducer (coke) in the presence of 7.5–12.5% CaCO₃ and 1.5–2% CaF₂ upon reducing roasting at a temperature of ≥1350°C. The yield of cast iron granules is 40–42.5% and the slag yield is 32–35% of the ore mass. 94–99% of iron and almost entire nickel are recovered into cast iron containing up 2.3% Ni and 2.1–2.5% C. The contents of the main components in the slag can change in the following ranges: 32–36% Al₂O₃, 17–24% CaO, 27–28% SiO₂, and 2.5–3.5 Fe_tot. The slag can be used as a combined flux addition for the reducing roasting of magnesia–silicate nickel ores in rotary hearth furnaces with the formation of ferronickel ball (Krupp–Renn process), which makes the technology of processing of hematite ores wasteless and economically efficient.

Abstract—The extraction of scandium from a nitric acid solution after pressure leaching of the hydrate cake that forms upon processing the ore of the Tomtor deposit is studied. The main technological laws of scandium sorption and extraction using various absorbers under static and dynamic conditions are investigated. To extract scandium, we recommend using phosphorus-containing cation exchanger Purolite D5041 and a mixture of extraction agents 7.5% Cyanex 923 + 15% tributyl phosphate in kerosene. The developed technologies make it possible to extract scandium and radioactive elements almost completely with the formation of a collective concentrate containing 2–3% Sc, 7–10% Th, and 0.3% U. Our data can be used to develop a technology of industrial scandium recovery after the extraction of thorium and uranium by the well-known methods.

Abstract—The low-cycle fatigue (LCF) of the single crystals made of a γ'-Ni₃Al-based VKNA-25 γ' + γ nickel superalloy is studied at 10⁴ cycles and a temperature of 20, 750, and 900°C. A temperature anomaly in the LCF fatigue limit of the VKNA alloy, namely, its increase with temperature in the range from 20 to 750°C, is detected. This anomaly is related to a change from octahedral to cubic slip at the temperature of the peak in L1₂-ordered alloys and to a change in the properties of the γ' and γ phases. At normal temperature, the static tensile strength and the LCF characteristics of the [111] single crystals are higher than those of the single crystals with other crystallographic orientations (CGOs). The static tensile strengths of the [001] and [111] single crystals at 900°C and the strengths of the single crystals with all CGOs at 1000°C are almost the same, and the LCF fatigue limit of the [001] single crystals at 900°C is slightly higher than that of the [111] single crystals.

Abstract—Thermodynamic analysis of the reduction of iron oxides in gas mixtures with H₂ and CO shows that the ratio of the reducibilities of these gases (γ) can decrease or increase with temperature or can be temperature-independent under different conditions. This contradicts the commonly accepted assertion that the reducibilities of H₂ and CO at 1093 K are equal and that the reducibility of H₂ increases with temperature when considering the intersection of the reduction curves and superimposing the equilibrium phase diagrams iron oxides–CO–CO₂ and iron oxides–H₂–H₂O. In this case, the parameters of a specific reduction technology, the composition of the formed water gas, and the possibility of soot carbon formation are ignored. In particular, when Fe₃O₄ is reduced to FeO in the presence of carbon in the temperature range 850–917 K and FeO is reduced to Fe in the range 850–955 K, the ratio of the reducibilities of H₂ and CO changes from zero to 5.76 depending on the temperature, the nature of the initial system, and its composition. It is shown that, for any technological organization, the reduction of Fe₃O₄ to FeO is characterized by γ = 1.71 in the presence of carbon at 917 K and the reduction of FeO to Fe at 955 K is characterized by γ = 2.30.

Abstract—The swelling of Kh18N9 steel fragments cut from the reactor internals after irradiation at 370–442°C and an atomic displacement generation rate of 4.8 × 10^–9–4.16 × 10^–8 dpa/s are determined by hydrostatic weighing. The vacancy migration energy for a Kh18N9 steel (1.24 eV) is estimated using the energies for austenitic steels (ChS68, EK164) with various nickel contents. The neutron irradiation-induced void growth in a Kh18N9 steel during its operation in the BN-600 nuclear power reactor internals is analyzed in terms of a point defect migration model with allowance for the estimated vacancy migration energy. The vacancy void growth rate at the beginning of the transient swelling stage is used as a characteristic of the susceptibility to radiation swelling. This rate is diameter independent for the samples under study.

Abstract—Changes in the magnetic properties of the sintered (Pr_0.76Dy_0.24)_12.9(Fe_0.53Co_0.47)_81.5B_5.6 material, which are caused by solid-phase alloying with the (Pr_0.63Dy_0.37)(Fe_0.31Co_0.69)₂B₂ alloy are studied. The dependences of the phase composition and the coercive force of the sintered material on the amount of the added alloy is obtained. As the boron content in the sintered material increases, the content of the main magnetic (Pr, Dy)₂(Fe, Co)₁₄B phase decreases from 89.2 to 51.4 vol % and the content of the (Pr, Dy)(Fe, Co)₃ phase increases from 7.1 to 43.9 vol %. It was found that, in the course of 190-h storage of sintered magnets in air, their coercive force and density are first unchanged and subsequently decrease; the coercive force decreases to zero.

Abstract—Allowing for the high prospects of the production of initial blanks for the rolling rings of gas turbine engines (GTEs) by centrifugal casting into shell molds and subsequent pulling of hollow blanks from a melt, we choose a forming scheme and temperature–deformation conditions at both final and preliminary stages of the technological cycle of rolling as-cast blanks made of titanium and nickel superalloys. The required service properties of the GTE rolling rings are found to be achieved upon rolling as-cast blanks subjected to preliminary deformation. The proposed method makes it possible to increase the ingot-to-product yield to 0.45–0.50 and to decrease the labor consumed for treatment and the cost of the GTE rings.