Composition and Mobility of Ionic Ensembles in Slags for Steel Refining in the Ladle–Furnace Unit

High-lime synthetic slags for refining steels in the ladle–furnace unit are investigated. The content of the slag mixtures is as follows: 60 wt % CaO, 7 and 8 wt % MgO, 7–23 wt % Al₂O₃, and 9–18 wt % SiO₂, with additions of 8 wt % CaF₃ and 5–15 wt % Na₂O. Polymer theory is used to calculate the composition of the anionic subsystem in the slag melts. The log-mean polymerization constants K _p ^* for multicomponent melts are calculated from the known polymerization constants in binary systems. It is found that K _p ^* ≈ 10^–3–10^–2 in the range 1500–1600°C. In that range, the melt’s degree of polymerization is 3 × 10^–4–8 × 10^–3. In the most polymerized melt, the ionic content of the dimers Si₂O ₇ ^6- and Al₂O ₇ ^8- is no more than 0.1 and 1.5% of the values for the corresponding monomers. Therefore, we assume, with an error of about 2%, that the structural units of the anionic subsystem are monomers AlO ₄ ^5- and SiO ₄ ^4- simple O^2– and F^– ions (slag 7). The cationic subsystem consists of Ca²⁺, Mg²⁺, Na⁺, and Al³⁺ ions in octahedral coordination with oxygen (less than 3% of all the Al atoms). In all the melts, the concentrations of free oxygen ions O^2– and Ca²⁺ ions are similar. In half the cases, the content of O^2– ions is greater than the content of Ca²⁺ ions. The mean mobility U and self-diffusion coefficient D for all the cations are calculated from data for the electrical conductivity and the density. With increase in temperature from 1500 to 1600°C, U and D increase by 50 and 60%, respectively, in all the slags. With increase in the mutual substitution of the components in the slag mixtures M = n(Na₂O, CaF₂)/n(Al₂O₃ + SiO₂), mol/mol, at 1600°C, U increases from 1.14 × 10^–8 to 1.46 × 10^–8 m²/(V s) for slags 1–6 (0 ≤ M ≤ 1.1) and from 1.01 × 10^–8 to 1.66 × 10^–8 m²/(V s) for slags 7–10 (0.25 ≤ M ≤ 0.65). Correspondingly, D increases from 9.2 × 10^–10 to 12.8 × 10^–10 m²/s for slags 1–6 and from 8.2 × 10^–10 to 14.3 × 10^–10 m²/s for slags 7–10. The temperature dependence of U and D may be approximated by an Arrhenius equation with activation energies E _U and E _D . With increase in M in the given ranges, E _U declines from 146 to 100 kJ/mol (slags 1–6) and from 124.5 to 109 kJ/mol (slags 7–10). Likewise, E _D declines from 159 to 116.5 kJ/mol (slags 1–6) and from 139.5 to 124 kJ/mol (slags 7–10). The mean values of E _U and E _D correlate with the mean distance between the cations in the melts. On the basis of the proposed alternative model of the conductivity, the O^2– ions may also transfer electric charge. Preliminary estimates show that the oxygen transport number at 1600°C may exceed 0.1 in some slags.     

Diffusion of copper along the grain boundaries in aluminum

The grain boundary diffusion (GBD) of copper in aluminum is investigated in the range t = 300?400°C. Investigations were performed on a scanning electron microscope equipped with an attachment for electron probe X-ray microanalysis. The triple product sδD _gb (where s is the segregation coefficient, δ is the width of the grain boundary, and D _gb is the GBD coefficient) was calculated by the Fisher criterion using two methods (namely, the copper concentration in the grain boundary, depending on the penetration depth, was determined and the angles in the vertex of the concentration profile was measured using an optical microscope). In the first case, sδD _gb was 5.1 × 10^?11 exp(?102/(RT)) m³/s; in the second case it was 1.4 × 10^?11 exp(?94/(RT)) m³/s. The obtained results are compared with innumerous literature data.     

Determination of the heat-transfer coefficient between the AK7ch (A356) alloy casting and no-bake mold

The heat-transfer coefficient h between a cylindrical cast made of AK7ch (A356) aluminum alloy and a no-bake mold based on a furan binder is determined via minimizing the error function, which reflects the difference between the experimental and calculated temperatures in the mold during pouring, solidification, and cooling. The heat-transfer coefficient is h _L = 900 W/(m² K) above the liquidus temperature (617°C) and h _S = 600 W/(m² K) below the alloy solidus temperature (556°C). The variation in the heat-transfer coefficient in ranges h _L = 900–1200 W/(m² K) (above the alloy liquidus temperature) and h _S = 500–900 W/(m² K) (below the solidus temperature) barely affects the error function, which remains at ~22°C. It is shown that it is admissible to use a simplified approach when constant h = 500 W/(m² K) is specified, which leads to an error of 23.8°C. By the example of cylindrical casting, it is experimentally confirmed that the heat-transfer coefficient varies over the casting height according to the difference in the metallostatic pressure, which affects the casting solid skin during its solidification; this leads to a closer contact of metal and mold at the casting bottom.     

Technology and properties of porous permeable aluminum-based materials

Results of the investigation of preparation conditions (pressure of powder pressing and time of sintering of compacts) and of the effect of aluminum additions (5–20 wt %) on the properties of a sintered porous material of an aluminum powder and its mixture with an Al₂O₃ powder are given. The possibility is shown of the production of porous (P = 30–35%), highly permeable (k = 2.0 to 2.5 × 10^?13 m²) aluminum-based sintered material with an addition of 20% Al₂O₃ and maximum size of pores equal to 1.3–1.5 μm in the following regime: p = 60 MPa, T = 723–823 K with an isothermal holding for 30–60 min.     

Oxidation of Aluminum Melts with Rare-Earth Metals

Thermogravimetry studies show that the oxidation of aluminum–rare-earth metal (R) melts obeys a parabolic law. The true oxidation rate of the melts is on the order of 10^–4–10^–3 kg/(m² s). In the Al–R systems, the minimum oxidation rate corresponds to the compositions of intermetallic compounds. The oxidation rate of a melt is shown to increase with temperature. It is found by IRS (infrared spectroscopy) and XRD (X-ray diffraction) that the melt oxidation products consist of γ-Al₂O₃, R₂O₃ (R = La, Ce, Pr, Nd, Y, Sc), CeO₂, and rare-earth metal monoaluminates RAlO₃ (CeAlO₃, LaAlO₃, NdAlO₃).     

Influence of heat treatment on the residual magnetization of steel in partial magnetic hysteresis

A formula is derived for the residual magnetization M_r of steel after repeated magnetic hysteresis, on the basis of measurements of the saturation magnetization M_s, the coercive force H_cs, the residual magnetization M_rs for the limiting hysteresis loop, and the maximum magnetizing field strength H_m of the partial hysteresis loop. The influence of variation in the tempering temperature t_te of steel on M_r at different H_m is analyzed. The dependence M_r(t_te) is established for small and large H_m. It is established that the M_r results may effectively be used for nondestructive assessment of the tempering of moderate-carbon alloy steel.     

Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis

Temperatures for primary crystallization of Na₃AlF₆ in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na₃AlF₆ was derived: $$\begin{gathered} t/(^\circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - \frac{{3.45[CaF_2 ]}}{{1 + 0.0173[CaF_2 ]}} \hfill \\ + 0.124[CaF_2 ] \cdot [AlF_3 ] - 0.00542([CaF_2 ] \cdot [AlF_3 ])^{1.5} \hfill \\ - \frac{{7.93[Al_2 O_3 ]}}{{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \cdot [Al_2 O_3 ]}} \hfill \\ - \frac{{8.90[LiF]}}{{1 + 0.0047[LiF] + 0.0010[AlF3]^2 }} - 3.95[MgF_2 ] - 3.95 \hfill \\ \end{gathered} $$ wheret is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na₃AlF₆-AlF₃-CaF₂-Al₂O₃-LiF-MgF₂-KF. The composition limitations are [AlF₃] ≈ [CaF₂] ≈ [LiF] < 20 wt pct, [MgF₂] ≈ [KF] < 5 wt pct, and [A1₂O₃] up to saturation.     

Influence of the Strengthening Curve on the Axial Stress in Round Rod on Drawing

For the drawing of round rod in conical drawplates, the boundary problem is solved on the basis of the Amontons–Coulomb frictional law for materials in which strengthening corresponds to the equation σ_s/σ_s0 = 1 + m(ln λ)ⁿ. The influence of the parameters m and n of the strengthening curve on the axial stress σ_x in the reducing section of the drawplate is established. The new result is compared with existing solutions. It is found that, if the strengthening law is replaced by approximate functions without taking account of the shape of the strengthening curve at small n, the calculated values of σ_x are too low, by 15–25%.     

Magnetic Hysteretic and Mechanical Properties of a 31Kh20K3M Alloy with an Increased Carbon Content

An Fe–31Cr–20Co–3Mo (31Kh20K3M) alloy containing 0.09 wt % C, which is almost twice as much as its maximum content according to GOST 24897–81, has been studied to verify the influence of the carbon content on the magnetic hysteretic properties of hard magnetic high-chromium Fe–Cr–Co alloys. The optimal heat treatment, including thermomagnetic treatment, results in the average values of residual magnetic induction B_r = 0.96 T and coercive force H_cB = 63 kA/m and the maximum energy product (BH)_max = 29 kJ/m³. Some heat treatment regimes give B_r = 1.03 T, H_cB = 72 kA/m, and (BH)_max = 31 kJ/m³. In addition, for isotropic alloy samples, the following average values are obtained: B_r = 0.71 T, HcB = 56 kA/m, and (BH)_max = 15 kJ/m³. These magnetic hysteretic properties of the 31Kh20K3M alloy with an increased carbon content are similar to those of a powder 30Kh21K3M alloy with the minimum carbon content.     

Thermomechanical and electrophysical properties of a solid electrolyte based on Na–β&quot;-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> with <Emphasis Type="Italic">t</Emphasis>-ZrO<Subscript>2</Subscript> additions

The strength, the fracture toughness, the thermal shock resistance, and the electrical conductivity of a ceramic Na–β"-Al₂O₃ solid electrolyte modified by t-ZrO₂ additions are studied. The influence of the reverse t-ZrO₂ → m-ZrO₂ transformation on the mechanical and functional properties of the ceramics is discussed. The ZrO₂ addition concentration is found to affect the sodium-ion conductivity of the solid electrolyte and its activation energy. The degree of defect accumulation in the ceramics modified by 8.5 wt % t-ZrO₂ is shown to decrease during a thermal shock.     

Liquid Inclusions in Heat-Resistant Steel Containing Rare Earth Elements

Abundant thermodynamic data of pure substances were incorporated in the coupled thermodynamic model of inclusion precipitation and solute micro-segregation during the solidification of heat-resistant steel containing rare earth elements. The liquid inclusions Ce_2x Al_2y Si_1?x?y O _z (0 < x < 1, 0 < y < x and z = 1 ? x ? y) were first introduced to ensure the model more accurately. And the computational method for generation Gibbs free energy of liquid inclusions in molten steel was given. The accuracy of accomplished model was validated through plant trials, lab-scale experiments, and the data published in the literature. The comparisons of results calculated by FactSage with the model were also discussed. Finally, the stable area of liquid inclusions was predicted and the liquid inclusions with larger size were found in the preliminary experiments.     

Effect of the severe plastic deformation temperature on the diffusion properties of the grain boundaries in ultrafine-grained metals

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)k _B T _m, which corresponds to the diffusion parameters of nonequilibrium grain boundaries, to (8–10)k _B T _m, which corresponds to the diffusion parameters of equilibrium grain boundaries (k _B is the Boltzmann constant, T _m 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.     

The Interface of TiB<Subscript>2</Subscript> and Al<Subscript>3</Subscript>Ti in Molten Aluminum

In the grain refinement of aluminum, Al₃Ti and TiB₂ particles are introduced to reduce the casting grain size down to 200 micrometer level, which makes cold working possible. The particles are brought in by the addition of Al-Ti-B-type master alloys. It is generally believed that TiB₂ particles are stable and nucleate α-Al grains in solidification in the presence of titanium in solution from the dissolution of Al₃Ti particles in the master alloys. The titanium in solution either forms Al₃Ti layers on the surface of TiB₂ particles to promote the nucleation of α-Al grains or remains as solute to restrict the growth of α-Al grains in solidification. However, a consensus on a grain refinement mechanism is still to be reached due to the lack of direct observation of the three phases in castings. This paper presents finding of the TiB₂/Al₃Ti interfaces in an Al-Ti-B master alloy. It demonstrates a strong epitaxial growth of Al₃Ti on the surface of TiB₂ particles, a sign of the formation of an Al₃Ti layer on the surface of TiB₂ particles in grain refinement practice. The Al₃Ti layer has a crystal coherency with α-Al and hence offers a substrate for heterogeneous nucleation of α-Al grains. However, the layer must be dynamic to avoid the formation of compounded Al₃Ti and TiB₂ particles leading to the loss of efficiency in grain refinement.     

Electrical conductivity of molten cryolite-based mixtures obtained with a tube-type cell made of pyrolytic boron nitride

A pyrolytic boron nitride tube-type cell was used to measure the electrical conductivity for molten cryolite, for binary mixtures of cryolite with Al₂O₃, AlF₃, CaF₂, KF, Li₃AlF₆, and MgF2, and for ternary mixtures Na₃AlF₆-Al₂O₃-CaF₂ (MgF₂) and Na₃AlF₆-AlF₃-KF (Li₃AlF₆). The cell constant was about 40 cm^?t. The temperature and concentration dependence of the conductivity in the investigated concentration range was described by the equation $$\begin{gathered} \kappa /S cm^{ - 1} = 7.22 exp\left( { - 1204.3/T} \right) - 2.53\left[ {Al_2 O_3 } \right] - 1.66\left[ {AlF_3 } \right] \hfill \\ - 0.76\left[ {CaF_2 } \right] - 0.206\left[ {KF} \right] + 0.97\left[ {Li_3 AlF_6 } \right] - 1.07\left[ {MgF_2 } \right] \hfill \\ - 1.80\left[ {Al_2 O_3 } \right]\left[ {CaF_2 } \right] - 2.59\left[ {Al_2 O_3 } \right]\left[ {MgF_2 } \right] \hfill \\ - 0.942\left[ {AlF_3 } \right]\left[ {Li_3 AlF_6 } \right] \hfill \\ \end{gathered} $$ whereT represents the temperature in Kelvin and the brackets represent the mole fractions of the additions. The standard deviation was found to be 0.026 S cm^?1 (～1 pct). For practical reasons, it is often desired to express composition in weight percent. In that case, it holds that $$\begin{gathered} \ln \kappa = 1.977 - 0.0200\left[ {Al_2 O_3 } \right] - 0.0131\left[ {AlF_3 } \right] - 0.0060\left[ {CaF_2 } \right] \hfill \\ - 0.0106\left[ {MgF_2 } \right] - 0.0019\left[ {KF} \right] + 0.0121\left[ {LiF} \right] - 1204.3/T \hfill \\ \end{gathered} $$ whereT represents the temperature in Kelvin and the brackets denote the concentration of the additives in weight percent. However, in this case, the maximum relative error of the conductivity equation can reach up to 2.5 pct.     

On the Nonequilibrium Interface Kinetics of Rapid Coupled Eutectic Growth

Nonequilibrium interface kinetics (NEIK) is expected to play an important role in coupled growth of eutectic alloys, when solidification velocity is high and intermetallic compound or topologically complex phases form in the crystallized product. In order to quantitatively evaluate the effect of NEIK on the rapid coupled eutectic growth, in this work, two nonequilibrium interface kinetic effects, i.e., atom attachment and solute trapping at the solid–liquid interface, were incorporated into the analyses of the coupled eutectic growth under the rapid solidification condition. First, a coupled growth model incorporating the preceding two nonequilibrium kinetic effects was derived. On this basis, an expression of kinetic undercooling (?T _k), which is used to characterize the NEIK, was defined. The calculations based on the as-derived couple growth model show good agreement with the reported experimental results achieved in rapidly solidified eutectic Al-Sm alloys consisting of a solid solution phase (α-Al) and an intermetallic compound phase (Al₁₁Sm₃). In terms of the definition of ?T _k defined in this work, the role of NEIK in the coupled growth of the Al-Sm eutectic system was analyzed. The results show that with increasing the coupled growth velocity, ?T _k increases continuously, and its ratio to the total undercooling reaches 0.32 at the maximum growth velocity for coupled eutectic growth. Parametric analyses on two key alloy parameters that influence ?T _k, i.e., interface kinetic parameter (μ _i ) and solute distribution coefficient (k _e ), indicate that both μ _i and k _e influence the NEIK significantly and the decrease of either these two parameters enhances the NEIK effect.     

Crystal and Electronic Study of Neodymium-Substituted CuFeO<Subscript>2</Subscript> Oxide

Neodymium-substituted CuFeO₂ samples were investigated according to their crystal and electronic properties via the general formula Nd _x Cu_1?x FeO₂. The crystal structure analysis results revealed polycrystalline formations in the sample and a change in crystalline sizes with the substituted heavy fermion “Nd.” Increasing the Nd amount in the sample was determined to cause a disturbance on the Cu-Fe planes that supports the formation of crystal structures with low crystal symmetries such as monoclinic or triclinic geometries. To obtain the background mechanisms of the crystal properties, the X-ray absorption fine structure spectroscopy technique was used to study the electronic properties of the samples. Prominent changes in the crystal structures due to 4f electrons’ contributions from the substituted Nd atoms as the main “role player” in the phase transitions were determined. The Nd atoms were observed as the key element guiding the entire phenomenon as a result of their large size and narrow 4f levels. Also, magnetic properties of the samples were tested at room temperature and without an applied magnetic field by X-ray magnetic circular dichroism study due to previous studies that reported the parent oxide CuFeO₂ to have magnetic ordering at T _N = 11 K (?262 °C). Except the sample for x = 1.0 (NdFeO₃), no magnetic ordering was observed at room temperature; i.e., all of the samples showed paramagnetic behaviors.     

Aging Temperature Dependence of <Emphasis Type="Italic">α</Emphasis>″-Martensite Decomposition Mechanism in Ti-Al-Fe-Si Alloy

The mechanism by which α″-martensite decomposes in Ti-4Al-4Fe-0.25Si-0.1O alloy is found to change depending on the aging temperature, with Fe-rich α first transforming in twins of α″-martensite. As the aging temperature increases, Fe is segregated at the boundaries between α″ and α. At temperatures >?773 K, the Fe-segregated boundaries provide a nucleation site for B2-structured TiFe intermetallic compounds. This process of α″-martensite decomposition is described as follows: α″?+?α″_Twin?→?α″_Fe-rich?+?α_Fe-rich,V1?→?α_Fe-lean,V2?+?α_Fe-lean,V1?+?TiFe.     

Energy consumption during in-plane rolling

The energy consumed for in-plane rolling is analyzed theoretically. The total energy consumption in a working stand a _st is differentially considered in the form of the following terms: the energies consumed for plastic deformation a _d, friction in roll bearings a _f, and for rolling friction in work and backup rolls a _r. Analytical dependences of the specific energy consumption on the plastic-deformation and working-stand parameters are proposed. The results calculated by these dependences agree with the experimental data measured on driven roll spindles.     

Construction of a mathematical model of sulfide sublimation of germanium from middlings

Based on empirical dependences of the value of a variable Y—the degree of sublimation of germanium (%) in the mode of sulfide melting (T = 1350°C, τ = 1 h)—on the values of the parameters that are characteristic of the content in charge, %, X ₁ × 10^?2, of the basicity {[CaO] + [MgO])/[SiO₂]}; X ₂ × 10^?3, of germanium; X ₃, of the slag-forming components (Σ[CaO], [MgO], [SiO₂]); X ₄, of carbon; and X ₅, of sulfur, by the method of computer mathematics with the use of the standard program packets Excel, Mathcad, and Maple, an adequate mathematical model of the influence of the charge composition on the degree of pyrometallurgical sublimation of germanium has been constructed.     

Equilibrium crystallization and distribution coefficients of alloy components in ternary systems with continuous solid and liquid solutions

Features of equilibrium crystallization of alloys in a ternary system consisting of solid and liquid solutions of components A, B, and C with melting points related as t _C < t _A < t _B are investigated in detail. It is demonstrated that, in alloys of any composition, the distribution coefficients of components B and C are k _B > 1 and k _C < 1, respectively. For the component A, this characteristic, depending on the alloy composition, can be either larger or smaller than unity, and at temperature t _A , k _A = 1.