Carbon Diffusion Measurement in Austenite in the Temperature Range 500 °C to 900 °C

Carbon diffusion in austenite plays a critical role in phase transformation in steel. However, it can only be estimated in the fully austenitic range and has then to be extrapolated to the temperature range of the phase transformation. Therefore, published data are limited to temperatures above 750 °C. In this study, new experiments are carried out to determine the carbon diffusion coefficient in austenite at temperatures as low as 500 °C. Carburization experiments are performed in the austenitic range for a Fe-1.5 pct Mn 0.13 pct C and a Fe-31 pct Ni alloy (wt pct). Composition profile measurements, which are done using glow discharge optical emission spectrometry (GDOES), show that the surface composition is not constant with time. A methodology has been developed to assess the diffusion coefficient of carbon in austenite combining the measured carbon profiles and a numerical method to compute the diffusion profile taking into account the time evolution of the boundary condition. This method is first validated on the Fe-C-Mn steel. Carburization experiments are carried out on a Fe-31 pct Ni alloy at 900 °C, 800 °C, 700 °C, 600 °C, and 500 °C. The carbon diffusion coefficient is assessed using the method described above and fitted with the following expression (T in Kelvin): \( D = 1.23\cdot10^{{ - 6}} \cdot e^{{ - \frac{{15,050}} {{T{\left( {\text{K}} \right)}}}}} ({\text{m}}^{{\text{2}}} {\text{/s}}) \). The new expression is compared with previous experimental results measured for comparable nickel content at higher temperatures, and it shows a reasonable agreement. The model proposed by Ågren for carbon diffusion has been modified to take into account the thermodynamic contribution of nickel. This model also shows good agreement with the present experimental results, even if it was fitted to experiments performed at higher temperatures.     

C-Ni and Al-C-Ni phase diagrams and thermodynamic properties of C in the alloys from 1550 °C to 2300 °C

The C-Ni and Al-C-Ni phase diagrams were determined by chemical analysis of alloys saturated with carbon within sealed graphite crucibles. The solubility of carbon in nickel over the temperature range 1550 °C to 2300 °C is given by log (at. pct C)=2.0376−1874.68/T, where T is temperature in kelvin. Isothermal sections for the ternary system were determined at intervals of 150 °C over the range of temperatures investigated. The univariant points on the 1700 °C, 1850 °C, and 2000 °C isotherms were determined by metallographic examination of rapidly cooled alloys to be about 67.2Al-1.1C-31.7Ni, 70.3Al-2.3C-27.4Ni, and 82.5Al-7.0C-10.5Ni, respectively, where all concentrations are in atomic percent. Graphite, Al₄C₃ (decomposition temperature 2156 °C), and AlNi (decomposition temperature 1638 °C) were the only solid phases observed within the temperature range investigated. The excess partial Gibbs energy for dissolved C, , in liquid Al-C-Ni solutions in equilibrium with C, as calculated from the experimental solubilities and thermodynamic data on Al-Ni, is

Cu-C and Al-Cu-C phase diagrams and thermodynamic properties of c in the alloys from 1550 °C to 2300 °C

The Cu-C and Al-Cu-C phase diagrams were determined at 1550 °C to 2300 °C by chemical and X-ray diffraction analyses of alloys saturated with carbon within sealed graphite crucibles. Isothermal sections for the ternary system were determined at intervals of 150 °C over the range of temperatures investigated. The univariant points in atomic percent on the 1700 °C, 1850 °C, and 2000 °C isotherms are 70.7Al-28.9Cu-0.4C, 74.4Al-24.0Cu-1.6C, and 78.3Al-17.0Cu-4.7C, respectively, as determined by metallographic examination of rapidly cooled alloys. Graphite and Al₄C₃ (decomposition temperature 2156 °C) were the only solid phases observed at these temperatures. The excess partial Gibbs energy for dissolved carbon in the liquid Al-Cu-C solutions in equilibrium with C, as calculated from the experimental solubilities, isˉ G _c ^e = - RT lnx =y ²[176,860 - 55.42T - (224,200 - 110.84T)x] +z ²[237,000 - 48.61T] +yz[320,510 - 36.77T + (30,180 + 35.10T)z + (51,570 - 74.13T)yz + (246,400 - 88.04T)yz ² - 60,000], J/g atom where R is the gas constant,T is the temperature in K, andx, y, andz are the atomic fractions of C, Al, and Cu, respectively. The equation also is a good approximation for liquid solutions in equilibrium with A1₄C₃.     

Determination of the Phase Equilibria in the Mn-Sn-Zn System at 500 °C

The isothermal section of the Mn-Sn-Zn system at 500 °C was determined with 20 alloys. The alloys were prepared by melting the pure elements in evacuated quartz capsules. The alloy samples were examined by means of X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. A new ternary phase Mn₄Zn₈Sn (λ) was found to have a bcc structure with a lattice parameter a = 0.92508 (5) nm. Its composition range spans 25 to 35 at. pct Mn, 4 to 8 at. pct Sn, and 55 to 70 at. pct Zn. The Zn is substituted for Mn in Mn₃Sn, Mn₂Sn, and Mn₃Sn₂. The solubility of Zn in Mn₃Sn, Mn₂Sn, and Mn₃Sn₂ was measured to be about 17, 12, and 4 at. pct, respectively. The phase boundaries of the liquid and β-Mn phases were well established. The following 3 three-phase equilibria were well determined: (1) β-Mn + ε-MnZn₃ + Mn₃Sn, (2) λ + Mn₃Sn + Mn₂Sn, and (3) L + λ + Mn₂Sn. The additional 5 three-phase equilibria, which are ε-MnZn₃ + λ + Mn₃Sn, ε ₁-MnZn₃ + ε-MnZn₃ + λ, ε ₁-MnZn₃ + λ + L, Mn₂Sn + L + MnSn₂, and Mn₃Sn₂ + MnSn₂ + Mn₂Sn, were deduced and shown with dashed lines in the present isothermal section.     

Mechanism of Low-Temperature Reduction Degradation of Alumina-Containing Hematite Solid Solution Below 550 °C

Metallurgical and Materials Transactions B - Low-temperature reduction degradation (LTRD) of sinter has an adverse effect on blast furnace permeability, and it is mainly caused by the stress...     

Study of creep deformation of irradiated zircaloy cladding by isothermal heating of irradiated PHWR fuel pins in temperature range 700°C–900°C

Fuel pins removed from actual irradiated fuel bundles discharged from Pressurised Heavy Water Reactors (PHWRs) have been used for experimental study of high temperature creep deformation as functions of cladding temperature and internal fission gas pressure. Experiment consisted of localized heating of 100 mm long segment of the fuel pins in a furnace in inert atmosphere at temperatures 700°C, 800°C, 850°C and 900°C for 10–15 minutes. The internal pressure and the total void volume in the fuel pins were estimated by puncture test on sibling pins from the same fuel bundle. After the heating experiment the diameter of the pin along the length was measured to obtain the diameter increase due to high temperature creep. Analysis of the experimental data for fuel pins with internal pressure 0.55 ± 0.05 MPa, provided the following empirical correlation for creep rate of the cladding as a function of temperature Creep rate (s^?1) = 2.23 × 10¹⁰ × exp (?305500/RT), for temperatures in the range of 800°C–900°C, where, R is gas constant, 8.314 J/mol K and T is temperature in K. For fuel pins with different internal fission gas pressures, the correlation obtained for the cladding strain as a function of internal pressure (at room temperature) was $$ \begin{gathered} Cladding strain = 118.22 \times 10^{ - 3} exp (0.53P), for temperature = 900^\circ C \hfill \\ where, P is the internal pressure in MPa at room temperature. \hfill \\ \end{gathered} $$ This paper presents the details of the experiment and the results.     

Distribution of Grain Boundary Carbides in Inconel 617 Subjected to Creep at 900 °C and 950 °C

Metallurgical and Materials Transactions A - A post-creep deformation analysis is carried out on the nickel-based superalloy Inconel 617 in order to identify the grain boundary carbide (GBC)...     

Phase equilibria in the tungsten-rich field of the W-Fe-Ni system in the 800–575°C

Conclusions In the W-Fe-Ni system subjected to annealing at 800 and 575°C, isostructural phases FeW and NiW form a continuous series of (Fe, Ni)W-type solid solutions.At 800 and 575°C, the phases NiW₂ and (Fe, Ni)W or a solid solution of nickel in the FeW phase are in equilibrium with the tungsten-based -solid solution and (Ni, Fe)W or a solid solution of iron in the NiW phase exists in equilibrium with the NiW₂ phase.It is assumed that an invariant eutectoid equilibrium + + (Fe, Ni)W exists in the system under study at a temperature of approximately 1130°C ( is the Fe₇W₆ phase; and and are the tungsten and the nickel-based solid solutions).Depending on the temperature, the phase composition of the binder present in the tungsten-based heavy alloys subjected to long-term annealing can undergo changes: at temperatures exceeding 1110°C, the binder consists of a nickel-based solid solution; in the 1100–1000°C range, an intermediate (Fe, Ni)W phase is present along with this phase; and at temperatures below 1000°C, it consists of the intermediate phases (Fe, Ni)W and NiW₂.Translated from Poroshkovaya Metallurgiya, No. 8(344), pp. 61–67, August, 1991.     

Construction of Al-based solid-solution range boundaries in the Al-Sc-Si system at 550 and 500°C

Electrical resistivity measurements and metallographic and electron microprobe analyses are used to study the Al-rich portion of the Al-Sc-Si system phase diagram at 500 and 550°C. The boundaries of the Al-based solid solution range are determined. The isothermal section at 550°C is constructed and the phases in equilibrium with the Al-based solid solution are determined.     

A Re-evaluation of the Solubility and Stability Regions of Calcium Arsenites and Calcium Arsenates in Aqueous Solution at 25°C

Abstract

The systems Ca(II)-As(III)-H₂O and Ca(II)-As(V)-H₂O were studied by equilibrating mixtures of calcium oxide and arsenious or arsenic acid solution at 25°C for one month. Where the pH of the final solution was likely to be greater than 8, care was taken to exclude atmospheric carbon dioxide. Chemical analysis of the final solid phases and the associated solution from each experiment for calcium and arsenic, together with X-ray diffraction analysis of the solids and an inspection of graphed relationships, indicated the existence of the compounds Ca(AsO₂)₂ and CaAsO₂OH 1/2H₂O in the system Ca(II)-As(III)-H₂O; and Ca(H₂AsO₄)₂, CaHAsO₄ H₂O, Ca₃(AsO₄)₂ 4H₂0 and Ca₂AsO₄OH 2H₂O in the system Ca(II)-As(V)-H2O. The solubility and stability regions for these compounds were assessed as a function of pH, and solubility constants and conditional free energies of formation for each compound calculated from the solubility data obtained.

A brief historical review of literature in which calcium arsenites and calcium arsenates have been reported is included in this paper.     

Electrochemical study of the catalytic influence of Sulfolobus metallicus in the bioleaching of chalcopyrite at 70 °C

The catalytic influence of Sulfolobus metallicus in bioleaching of chalcopyrite at 70 °C and pH 1.7 was characterized from studies of anodic dissolution of a chalcopyrite concentrate at constant potential. Experiments were conducted in iron-free nutrient medium which minimized the influence of jarosites formation on the process. The use of a novel electrochemical technique enabled the simultaneous determination of copper dissolution rate and the number of electrons involved in the dissolution reaction. This experimental approach permitted to monitor the degree of the oxidation of reduced sulfur compounds and assess its influence on the copper dissolution kinetics.Experimental results showed that in bioleaching of chalcopyrite with S. metallicus there is an efficient process of oxidation of residual sulfur compounds, i.e. sulfur and polysulfides, formed during the chemical dissolution of the sulfide. This oxidative process contributes to a dramatic increase in copper dissolution rate with respect to that obtained in chalcopyrite dissolution under simple indirect bacterial action. Oxidation of reduced sulfur compounds in the presence of S. metallicus involves the participation of a mechanism of chemical catalysis triggered by the presence of dissolved oxygen in solution.     

Solubility of silver in the K–KCl melt at 850°C

The solubility of silver in K–KCl melts at 850°C is studied in varying the potassium content from 0 to 100 mol %. It is shown that the solubility linearly increases as the alkali metal content increases; the solubility of silver in potassium melt is 6.0 mol %.     

Interdiffusion in Ni-rich,Ni-Cr-Al alloys at 1100 and 1200 °C: Part II. Diffusion coefficients and predicted concentration profiles

Ternary interdiffusion coefficients were measured in the Ni solid solution γ (fcc) phase of the Ni-Cr-Al system at 1100 and 1200 °C. Extensive use was made of both γ/γ and γ/γ + β (β-NiAl structure) diffusion couples. Two analysis techniques were employed to calculate the interdiffusion coefficients. When the Matano planes for Al and Cr were not coincident, numerous integral calculations were made to determine an average diffusion coefficient and to assess the effect of the noncoincidence of the Matano planes. The results of the diffusivity measurements showed that is approximately four times greater than , while and are of the same magnitude. For all concentrations, is two to three times greater than . Both and increase with increasing Al concentration, whereas and show little concentration dependence on Cr alone. A ternary, finite-difference interdiffusion model was employed to predict concentration profiles for the γ/γ couples utilizing the concentration dependence of the measured diffusivities. Good agreement was observed between the predicted and measured concentration profiles for both 1100 and 1200 °C.     

Solubility limit for sulphur in nickel between 637° and 1400° C

Abstract

The activity of sulphur in α -solid nickel and the solubility limit of sulphur in solid nickel with respect to liquid nickel sulphide has been determined in the range 850° to 1400°C by equilibration of dilute alloys with H₂S/H₂ mixtures. Estimates of the solubility limit down to the eutectic at 637°C have been obtained by extrapolation and from mechanical tests. The solubility limit is retrograde. At the solubility limit maximum near 1250°C it takes the value 430 ± 50 wt ppm and at the eutectic temperature of 637°C it is inferred to be 20 ± 12 wt ppm. The standard free energy change for the reaction

H₂S ? H₂ +S (in solid Ni)

based on a standard state of 1 atomic per cent sulphur in solid nickel is

?F^o= 6070 ? 10.13T

Résumé

Les auteurs ont déterminé la solubilité du soufre dans Ie nickel α et les limites de solubilité du soufre dans Ie nickel solide en équilibre avec du sulfite de nickel liquide dans un domaine de tampérature de 850 à 1400°C en amenant à équilibre les alliages avec un mélange H₂ S/H₂. Des estimés de solubilite jusqu'a l'eutectique, à 637°C, ont pu etre obtenus par extrapolation et par des essais mécaniques. La limite de solubilité est inverse at à son maximum, vers 1250°C, elle est de 430 ± 50 ppm poids et à la température de l'eutectique, 637°C, elle est estimée à 20 +m; 12 ppm poids. L' énergie libre normale de la réaction

H₂S ? H₂ +S (dons Ni sol)

basée sur un état standard de 1%at. S dans le Ni sol. est

?F^o= 6070 ? 10.13T     

Section of the isothermal tetrahedron of the Al-Cu-Mg-Zr phase diagram at 490°C

The phase equilibria in the Al-Cu-Mg-Zr system at 490°C have been studied for Al-rich alloys with 0.3% Zr and from 0 to 10% Cu or Mg. The (Al) solid solution is found to be in equilibrium with only binary θ(CuAl₂) and ZrAl₃ and ternary S (CuMgAl₂) phases of the ternary Al-Cu-Mg system. The section of the isothermal tetrahedron of the Al-Cu-Mg-Zr phase diagram at 490°C, which corresponds to 0.3% Zr and up to 10% Cu or Mg, is constructed.