Isotherm velocity in the axial zone of a continuously cast steel ingot

The behavior of the isotherm velocity in a continuously cast solidifying steel ingot is analyzed. An expression is obtained to describe the accelerated motion of isotherms near the thermal center of a cooled body (the center of symmetry of the body) without a phase transition. In the axial zone of the solidifying ingot, where the thermal overheating is insignificant, the isotherm velocity is caused by the action of two opposing factors: (i) the accelerated motion of isotherms that is characteristic of bodies cooled without a phase transition when the thermal center is approached and (ii) the release of the heat of phase transition. As a result, in the axial zone of an ingot made of a low-carbon steel (the initial carbon concentration C ₀ ≤ 0.2%), the liquidus isotherm velocity is almost constant, whereas the isotherm motion at the end of solidification is sharply accelerated, as in the case of purely thermal cooling. For high-carbon steels (C ₀ ≥ 1.0% C), the liquidus isotherm velocity increases, and the velocity of the isotherm at the end of solidification is constant (the effect of the eutectic transformation manifests itself). As a consequence, in low-carbon steels, the pool calculated from the liquidus and pouring-boundary isotherms has the shape of an acute-angled wedge, and the pool calculated from the isotherm of the end of solidification has a rounded shape. In contrast, in high-carbon steels, the pool shape calculated from the liquidus and pouring-boundary isotherms is rounded, and the pool shape calculated from the isotherm of the end of solidification is wedgelike. As a result of the analysis, a mathematical procedure is proposed for the calculation of the isotherm velocity in the two-phase zone and the shape and position of the pool bottom (from the corresponding isotherms) in a continuously cast solidifying steel ingot.     

Machinability of the high-strength corrosion-resistant high-ductility austenitic steel 06Kh22AG15N8M2F

The machinability of the high-nitrogen corrosion-resistant austenitic steel 06Kh22AG15N8M2F during turning is studied. The specific features of the structure of the surface layers in steel workpieces after turning are revealed. The cutting conditions that provide the lowest wear of VK8 alloy cutting tools upon turning are found: the cutting speed is 21–74 m/min, the feed is 0.15–0.60 mm/rev, and the cutting depth is 0.15–0.75 mm. The presence of a large amount of Cr₂N-type chromium nitrides in the structure of the steel annealed at 800°C for 2 h and a high nitrogen content in the austenite of the steel quenched from 1100°C increase the wear of the cutting tools. As to turning of the forged steel, the wear resistance of the cutting tools upon turning of the 06Kh22AG15N8M2F steel is higher than that upon turning of 08Kh18N10T steel, in which deformation martensite forms (in surface layers) during turning.     

High-plasticity heat-resistant 03Kh14G16N6Yu-type steels with heat-and deformation-resistant austenite

The structure and mechanical properties of 03Kh14G16N6Yu-type austenitic steels alloyed by molybdenum, tungsten, vanadium, and zirconium are studied after normalization at 1075°C and long-term holding at 500–700°C. The chemical composition of these steels ensures the resistance of their austenite to the martensitic transformation in the temperature range from 1200 to ?196°C and during cold plastic deformation at a reduction of up to 60%. The best combination of the mechanical and technological properties is achieved in a 03Kh15G17N6YuVF steel with 0.08% W and 0.12% V. Long-term (up to 1000 h) holdings at 550–750°C do not cause the precipitation of carbide, nitride, and intermetallic phases in this steel. The long-term strength of the 03Kh15G17N6YuVF steel at temperatures up to 650°C is comparable with and its plasticity and impact toughness are higher than those of high-nickel Kh16N9M2 and Kh16N12M2 steels, which are applied in the main parts of electric power installations.     

Processing of the rebellious polymetallic filizchai deposit ore using a combined technology

The results of studying the processing of rebellious polymetallic ores by a combined method are presented. The method combines the pyrometallurgical (pyrrhotinizing roasting) and hydrometallurgical (autoclave leaching with sulfuric acid) approaches. The proposed technology makes it possible to substantially enhance the degree of extraction of valuable components, simultaneously satisfying the requirements of the complex use of raw materials and the preservation of the environment.     

Corrosion resistance of vanadium alloys clad by a ferritic corrosion-resistant steel in liquid-metal heat-transfer agents

The results of studying the corrosion resistances of steels of various classes and vanadium-based alloys in liquid-metal heat-transfer agents (lithium, sodium, lead) are analyzed. These structural materials are shown to have satisfactory corrosion resistance in high-purity liquid metals. However, a nitrogen impurity in lithium and an oxygen impurity in sodium and lead cause the degradation of the mechanical properties and the fracture of the vanadium alloys. The use of these alloys clad by a ferritic corrosion-resistant steel is shown to ensure high corrosion resistance of the fuel-element can materials in fast neutron reactors with sodium and lead heat-transfer agents.     

Effect of mechanical activation on the characteristics of ruthenium and aluminum powder mixtures

The effect of treatment in a high-energy mill-attritor on the structure of RuAl-based alloy powder mixtures and the exothermic effects in them is studied. The mechanical activation (MA) of aluminum and ruthenium powder mixtures is found to mill the conglomerates of hard disperse (0.5–2 μm) ruthenium particles in the initial mixtures and to produce composite granules. These granules consist of hard disperse ruthenium particles connected by plastic fcc aluminum particles. The structure of these granules differs from that of the layered granules that form during the MA of powder mixtures of two plastic fcc metals (nickel, aluminum). The cold working of the hard ruthenium particles, which have the hcp lattice and are deformed via twinning, occurs due to a decrease in the coherent domain size (to 120–80 nm) rather than to an increase in the dislocation density (as in the case of the MA of Ni-Al powders). Every granule contains all alloy (composite) components, including disperse or nanosize oxide particles, bound to the components that form an intermetallic matrix during reaction sintering. In granules of both types, MA increases the contact area between both metals entering into the reaction of RuAl (NiAl) formation and sharply decreases the diffusion path length of Al in Ru (Ni). This results in a decrease in the temperature of the onset of reaction alloy formation, which begins now in a solid phase, and in a decrease in the exothermic effect of the monoaluminide formation with the participation of a liquid phase (Al). MA for 15–16 h of powder mixtures provides a microuniform distribution of base and alloying elements and phases in the deformable alloys with an intermetallic matrix that are produced by reaction sintering.     

Mechanism of the effect of the ferrite grain size on the fatigue strength of a low-carbon steel

The effect of the ferrite grain size on the fatigue strength of a low-carbon steel is studied. It has been shown that, as the ferrite grain size increases, the fatigue strength decreases due to plastic-flow localization. One of the explanations of this phenomenon is the beginning of the formation of periodical cellular dislocation structures.     

Role of silicon in the formation of the corrosion resistance of austenitic materials for cryogenic engineering

The effect of silicon on the operational efficiency and corrosion resistance of low-temperature equipment made of 12Kh18N12T chromium-nickel steel has been studied. The specific features of the cryogenic equipment consist in high-temperature heating procedures between operation periods. Equipment for gas liquefaction and cleaning aimed at the restoration of the operational efficiency of filtration and catalysis systems serves as an example. The heating temperature of this equipment can reach 800°C. Experimental steels containing 0.09–1.03 wt % Si are subjected to intercrystalline corrosion tests. Upon heating to 550–600°C, silicon is found to increase the corrosion resistance of the steel, and, upon heating at higher temperatures, silicon plays a negative role. This is caused by the distribution of silicon atoms along grain boundaries, namely, a nonuniform silicon distribution with the formation of high-and low-concentration regions, i.e., the formation of clusters of silicon-phase preprecipitates.     

Behavior of carbon,oxygen, and sulfur during hydrogen blowing of liquid steel

The decarburization of liquid steel during hydrogen blowing has been studied. The decarburization is caused by the interaction of carbon with oxygen dissolved in the metal. As the melt is blown with hydrogen, the decarburization is enhanced owing to hydrogen bubbles, which increase the effect of mixing of a metal bath and substantially increase the melt-gas phase interface. As a result, the rate and completeness of decarburization increase significantly. It is experimentally shown that hydrogen blowing of a melt substantially decreases the sulfur concentration in the metal because of the interaction of hydrogen with sulfur.     

Atomic ordering in the phases of a nickel-chromium-based superalloy

The distribution of alloying atoms over the sites of the ordered crystal lattices of the γ′ phase and the Ni₂Cr superstructure that form during aging of the EK78 superalloy is determined by neutron diffraction, and their long-range order parameters are measured. The size, shape, and orientation of the forming γ′-phase precipitates and the ordered matrix are determined by electron microscopy. The mechanism by which the ordered phases in the EK78 alloy form during complex heat treatment is described.     

Use of phase diagrams for the prediction of the ferrite-and silicate-binder compositions of fluxed sinters

The compositions of the calcium aluminosilicatoferrite phases in commercial iron-ore sinters, which are solid solutions based on CaFe₄O₇, CaFe₂O₄, and Ca₂Fe₂O₅ ferrites of the CaO-Fe₂O₃ system, are studied. The sequence of the formation of the calcium aluminosilicatoferrites and their compositions with Ca₂SiO₄ and Ca₃SiO₅ silicates in sinters is found to be analogous to the crystallization of the ferrite and silicate phases in the ternary CaO-SiO₂-Fe₂O₃ system. This allows the phase diagram of this system to be used for the explanation of the formation of the mineral binder compositions for ore grains during sintering of commercial superfluxed sinters.     

Reliability of the thermodynamic data obtained using the Gibbs-Duhem equation for ternary systems

The reliability of the thermodynamic data obtained by the Gibbs-Duhem equation for binary systems is analyzed, and the testing of this reliability is shown to be highly efficient. A similar testing technique is developed for a ternary system, and the application of this technique to a model system supports its validity and efficiency. The use of the developed technique for testing the data for the ternary Cd-Bi-Pb system of metallic melts confirms its validity and efficiency.     

X-ray diffraction study of the structural evolution in a grade 1469 (Al-Cu-Li) alloy during the production of hot-rolled sheets

X-ray diffraction is used to study the structural changes in a grade 1469 (Al-Cu-Li) alloy with a high lithium content that occur during the production of hot-rolled sheets according to the ingot → pressed strip → hot-rolled sheet schedule. In the pressed strip, a multicomponent Bs {110}〈112〉, Cu {211}〈111〉, and S {123}〈111〉 texture forms, which is typical of articles pressed from such alloys, and an unusual intense single-component texture of the Ex₁ {011}〈111〉 type forms in the hot-rolled sheets. Its formation is stimulated by cross rolling of the sheets. The low strength characteristics of the hot-rolled sheets after heat treatment are related to an elevated heating temperature used for quenching and to the oriented precipitation of the lamellar particles of the hardening T ₁ phase.     

Deposition from the two-phase multicomponent flow of a vacuum-arc plasma containing droplets of an evaporated material

The interaction of a surface with the two-phase flow of a multicomponent vacuum-arc plasma containing droplets of an evaporated material along with multicharged ions and neutral atoms is studied. For the two-phase flow of a multicomponent plasma, the dependences of the ion-current density, the deposition rate, and the heat flow to a substrate on the bias voltage are obtained, and the conditions at which the coating deposition rate is inverted are determined. A unique probe technique for the plasma flow generated by an end-face Hall plasma accelerator with a “cold” eroded cathode is used to determine the volt-equivalent energy U** of the interaction of the two-phase plasma flows of Ti, Al, Cr, and an Ni-Cr-Al-Y alloy with a surface and the self-sputtering coefficient of the Ni-Cr-Al-Y alloy and its elements (Ni, Cr, Al) as a function of the bias voltage. Metallographic analysis is used to study the structure of thick (～100-μm) coatings deposited from the two-phase flow of a metallic multicomponent vacuum-arc plasma.     

Applicability of the laws of elasticity for the determination of the elastic-region length in the deformation zone during cold rolling

The errors of calculating the energy-force parameters of cold rolling are analyzed. They appear because of the assumption of the classic rolling theory about the applicability of the Hertz formula, which is known in the theory of elasticity, to the calculation of the elastic-region length in the deformation zone. The Hertz formula, which is used to calculate the half-width of the contact area between a fixed cylinder and a plane that bounds an elastic half-space, is shown not to take into account the following factors that are characteristic and important for the roll-strip contact: the cold working of the strip, the strip thickness, the rotation of rolls accompanied by sliding friction, and the wear that decreases the initial roll roughness (i.e., changes in the friction coefficient). A method is proposed for taking into account these factors in the calculation of the energy-force parameters of cold rolling; it is based on the statistical processing of the parameters that are measured in operating mills and are present in the databases of their process control systems. The application of this method decreases the errors of calculating the rolling forces by 35–40% and refines some laws of the state of stress in a rolled strip.     

X-ray technique for the estimation of residual stresses after shot-blasting metal forming

A technique is developed for the correction of the depth distribution of residual stresses measured by an X-ray method with allowance for their relaxation upon the removal of surface layers. This technique is applied to the study of a D16 aluminum alloy strip subjected to shot-blasting metal forming. This technique can be used to estimate the distribution of residual stresses across massive parts after various types of treatment.     

Chemical compatibility of a TiAl-Nb melt with oxygen-free crucible ceramics made of aluminum nitride

The problem of uncontrolled oxygen contamination of intermetallic TiAl ingots is considered for the application of crucibles and molds based on traditional oxide ceramics. A synthesized Ti-45.9Al-8Nb (at %) alloy is solidified in alternative oxygen-free crucibles made of high-purity aluminum nitride (99.99% AlN) upon holding at 1670°C for 5, 12, and 25 min and subsequent quenching in a high-purity argon atmosphere. The initial material and the solidified ingots are studied by scanning electron microscopy, optical microscopy, X-ray diffraction, electron-probe microanalysis, and gas-content chemical analysis. The key features of the interaction of the TiAl-Nb melt with AlN ceramics are revealed. Partial thermal dissociation of the crucible material according to the reaction AlN → Al + N and the reaction of atomic nitrogen with the melt lead to the formation of a solid 6.4-μm-thick TiN coating on the ingot surface and provide perfect wettability of the crucible by the melt and easy removal of solidified casting items from the mold. The TiN coating serves as a diffusion barrier that hinders the diffusion of nitrogen and residual oxygen from the pores in the crucible toward the melt. As a result, no oxide particles are detected in the ingots. However, few single microprecipitates of two nitride phases ((Ti,Al) _x N _y , NbN) are detected in the near-bottom region, 300 μm thick, in the alloy after holding at 1670°C for 25 min. The total oxygen contamination in a two-phase α₂ + γ ingot does not exceed 1100 wt ppm, which is 1.5–2 times lower than that obtained in the experiments performed with modern advanced oxide crucibles made of yttrium ceramics Y₂O₃. AlN is shown to be a promising crucible material that can be considered as an alternative to oxide ceramics in the metallurgy of TiAl intermetallics.     

Autoclave processing of the products of catalytic synthesis of industrial diamonds

A process is developed for the autoclave leaching of nickel and manganese with sulfuric acid from the products of catalytic synthesis of industrial diamonds containing 20% Ni and 30% Mn. The optimum conditions for the autoclave processes are determined to be as follows: the temperature range is 150–160°C, the solution acidity is 5 N H₂SO₄ (230–240 g/l), the leaching duration is 2 h, and the number of processing steps is two. The extraction of the metals into a solution under these conditions is >99% for a total Ni + Co content of <0.4–0.5% in the autoclave leaching cake. The studies performed are related to the search for alternative ways of the catalytic preparation of industrial diamonds that can replace the nonferrous metal leaching technology using aqua regia solutions, which is mainly applied for these purposes under industrial conditions.     

Thermodynamic properties of liquid alloys of the Ni-Hf system

By the method of calorimetry in isoperibolic conditions are determined integral and partial mixing enthalpies of liquid alloys of the Ni-Hf system at 1770 ± 5 K. Defined that liquid Ni-Hf alloys are formed with allocated large quantity of heat. The analysis of own and literary data has allowed to establish for mixing enthalpies of binary Ni-Hf liquid alloys dependence on temperature. With use of the Schröder equation are calculated the activities of studied alloys components from co-ordinates of liquidus line of the phase diagram of this system. Between calculated and experimentally established values of melts components activities of the Ni-Hf system is observed only qualitative consent. Are also calculated ΔG and ΔS of liquid Ni-Hf alloys.     

Mechanism of the structure formation of the transition layers in cobalt films electroplated on copper

The structure formation of the transition layers in electrolytic cobalt films on copper substrates is studied. It has been found that epitaxial growth and repeated twinning in the transition film/substrate layers form the nonequilibrium α and β cobalt phases, which cause additional reflections in electron and X-ray diffraction patterns.