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Vol 2017, No 5 (2017)
- Year: 2017
- Articles: 11
- URL: https://journals.rcsi.science/0036-0295/issue/view/10446
Article
Phase transitions during reducing roasting of a leucoxene concentrate with carbon
Abstract
The phase transitions during the reducing roasting of a leucoxene concentrate with carbon are studied to obtain an anosovite product. Thermodynamic modeling of the reducing roasting is performed, and the influence of the temperature and the amount of a reducing agent on the reduction of rutile to Ti3O5-based anosovite is studied. Almost complete reduction of rutile to anosovite occurs in a temperature range of 1350–1400°C in the presence of 2.5–5.0% carbon. The Magnéli phases of various compositions are predominantly formed at lower temperatures and smaller amounts of the reducing agent. At temperatures higher than 1400°C and a reducing agent amount >2.5%, rutile reduction results in the formation of anosovite along with an undesirable titanium carbide phase.
357-361
Effect of addition of silicate and aluminosilicate fluxes on structure and phase composition of chromium sinter
Abstract
The microstructure of the fluxes (aluminosilicate clays) tested during pilot sintering of the chromium ore fines of the Don ore-dressing and processing enterprise is studied. The composition of the liquid phase that forms upon softening of materials and bonds chromospinelide grains is analyzed by chemical, electron- probe, and X-ray diffraction analyses. The results demonstrate that the clays have a similar morphology and differ substantially in the phase composition of both the initial fluxes and the binder in the composition of the chromium ore sinter with clay additions. The phase composition of the binder formed upon addition of aluminosilicate clays is compared with the application of an anthropogenic silica-containing flux (microsilica). A relation between the phase composition of the initial fluxes and the aluminosilicate binder in the composition of chromium sinter is found, and the advantages of aluminosilicate clays are demonstrated.
362-371
Construction of viscosity diagrams for CaO–SiO2–Al2O3–8% MgO–4% B2O3 slags by the simplex lattice method
Abstract
The simplex lattice method of planning experiments is used to study the viscosities of CaO–SiO2–Al2O3–8% MgO–4% B2O3 slags in a wide chemical composition range. For each viscosity, we developed an adequate mathematical model in the form of a reduced third-order polynomial. The results of mathematical simulation are presented in composition–viscosity diagrams. Composition regions with a high fluidity of slags, the viscosities of which are 0.8–1.2 Pa s in the temperature range 1500–1600°C, are indicated in the diagrams.
372-375
Effect of liquid–solid pouring on the as-cast structure and the distribution of nonmetallic inclusions in a 24.2-t steel 38KhN3MFA ingot
Abstract
The primary dendrite structure and the distribution of nonmetallic inclusions in large-scale 24.2-t forging ingots of 38KhN3MFA steel cast by a standard technology and with the inoculation of a metallic stream are studied. The dendrite parameter in the inoculated ingot is found to be significantly smaller than that in the usual ingot. Therefore, the solidification process in the inoculated ingot should be faster than that in the usual ingot. This is confirmed by a more homogeneous dendrite structure of the inoculated ingot. The estimation of contamination with nonmetallic inclusions shows that nonmetallic inclusions in the ingots under comparison are of the same type, and among them are oxides, sulfides and oxysulfides. The study of the distribution of nonmetallic inclusions shows that the ingots to be compared are mainly contaminated with oxysulfide nonmetallic inclusions, and the contents of oxide and sulfide nonmetallic inclusions are minimal. The experimental ingot has lower total contamination with nonmetallic inclusions than that of the reference ingot. In this case, the inoculators having formed from a metallic melt stream do not favor an increase in the contamination of steel with nonmetallic (among them are oxide) inclusions. The study of the structure of large metal volumes shows that the inoculation of the stream is accompanied by an increase in the number of metallic droplets, which transform into solid particles in flight and increase the solidification rate when reach a solidifying ingot. This process suppresses the development of segregation phenomena in the cast metal and decreases the chemical and physical heterogeneities.
376-383
Surface stresses in plastically deformed steels by X-ray diffraction
Abstract
Surface stresses in samples of wheel steel with different degree of plastic deformation are studied. Both surface stresses and the microstructure of the steel are changed in the dependence on the plastic deformation magnitude. The X-ray technique is shown can be used to study a change in the surface stresses due to development a plastic deformation under action of operating loads.
384-389
Finite element simulation of microindentation
Abstract
Finite element models are created to describe the testing of a material by a Berkovich indenter. The results of calculations by these models are compared to experimental data on indentation of the same material (grade 10 steel). The experimental and calculated data agree well with each other. The developed models for an indenter and the material to be tested are used to find the laws of behavior of a material during indentation. The state of stress in the material under an indenter is studied by various methods. The indentation results are plotted versus the mechanical properties of a material.
390-396
Primary radiation damage of an FeCr alloy under pressure: Atomistic simulation
Abstract
The primary radiation damage of a binary FeCr alloy deformed by applied mechanical loading is studied by an atomistic molecular dynamics simulation. Loading is simulated by specifying an applied pressure of 0.25, 1.0, and 2.5 GPa of both signs. Hydrostatic and uniaxial loading is considered along the [001], [111], [112], and [210] directions. The influence of loading on the energy of point defect formation and the threshold atomic displacement energy in single-component bcc iron is investigated. The 10-keV atomic displacement cascades in a “random” binary Fe–9 at % Cr alloy are simulated at an initial temperature of 300 K. The number of the point defects generated in a cascade is estimated, and the clustering of point defects and the spatial orientation of interstitial configurations are analyzed. Our results agree with the results of other researchers and supplement them.
397-405
Modifying ability of titanium-based pelleted master alloys
Abstract
The problem of enhancing the quality of pressed titanium master alloys is discussed to increase the rate and degree of dissolution of their components and to ensure the formation of a fine-grained structure in aluminum alloys. A technology of producing a pelleted titanium master alloy for effective correction of the chemical composition of an aluminum alloy in casting is developed and tested. Incoming inspection of the component composition and the flux distribution in the volume of pressed pellets of various manufacturers is performed. The rate of dissolution of pressed powder master alloys in the aluminum melt is studied, and their modifying ability is estimated after studying the microstructures of cast blanks. Molasses is used as a binder in a pelleted master alloy. As a result, we achieved a uniform flux distribution over the pellet volume and the formation of uniform pores after annealing as compared pelleted master alloys of other manufacturers. The fabricated alloying briquettes have higher strength characteristics and their dissolution rate in the aluminum melt is higher than those of analogs by 15–20%.
406-412
Effect of the severe plastic deformation temperature on the diffusion properties of the grain boundaries in ultrafine-grained metals
Abstract
A model is proposed to explain the effect of the severe plastic deformation (SPD) temperature on the diffusion properties of the grain boundaries in ultrafine-grained (UFG) metals and alloys. It is shown that an increase in the SPD temperature in UFG metals leads to an increase in the activation energy of grainboundary diffusion from (3–5)kBTm, which corresponds to the diffusion parameters of nonequilibrium grain boundaries, to (8–10)kBTm, which corresponds to the diffusion parameters of equilibrium grain boundaries (kB is the Boltzmann constant, Tm is the melting temperature). The dependence of the activation energy of grain-boundary diffusion on the SPD temperature is found to be determined by the kinetics of the competing processes of defect accumulation at grain boundaries and the diffusion accommodation of defects.
413-425
Multilayer metallic material with specific properties and the technology of its production
Abstract
A new class of multilayer materials with an internal protector and high corrosion resistance is proposed. A new principle of pitting corrosion protection is suggested. The choice of selecting the layers in multilayer materials intended for ooperation in oxidizing and nonoxidizing media is grounded. The fields of application of the multilayer materials are specified.
426-431
Manufacture of NiAl-based rods for plasma centrifugal spraying using mechanochemical synthesis
Abstract
An alternative technology is proposed for the production of NiAl–Co–Cr–Hf–Al2O3 alloy rods. It includes the fabrication of a powder by mechanochemical synthesis (MCS) followed by hot isostatic pressing in forming tool. The processes of MCS of the intermetallic alloy in a planetary mill and an attritor are studied. The products of synthesis in various mixers are compared. The microstructure and the properties of compacted samples are studied: their ultimate compressive strength is 1390–1480 MPa at a plasticity of 8.5–8.8%. Spherical granules with a target size of 20–200 μm are fabricated by plasma centrifugal spraying of the rod workpiece formed by the proposed technology.
432-440