Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1993"

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CaO-Al 2 O 3 , Al 2 O 3 -SiO 2 , and CaO-Al 2 O 3 -SiO 2 systems

Abstract: All available thermodynamic and phase diagram data have been critically assessed for all phases in the CaO-Al2O3, Al2O3-SiO2, and CaO-Al2O3-SiO2 systems at 1 bar pressure from 298 K to above the liquidus temperatures. All reliable data for the binary systems have been simultaneously optimized to obtain, for each system, one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. With these binary parameters and those from the optimization of the CaO-SiO2 system reported previously, the quasichemical model was used to predict the thermodynamic properties of the ternary slag. Two additional small ternary parameters were required to reproduce the ternary phase diagram and ternary activity data to within experimental error limits. The calculated optimized phase diagram and thermodynamic properties are self-consistent and are the most reliable currently available estimates of the true values.

The density of liquid iron-carbon alloys

Abstract: The density of liquid Fe-C alloys at temperatures ranging from 1250 °C to 1550 °C was measured by the sessile drop profile method. An accurate method of digital image processing was de-veloped to capture, enhance, and determine the coordinates of the X-ray shadow image of the droplet. Laplace's equation was then solved to obtain the volume and density of the droplet. The density of iron-carbon alloys was then determined as a function of carbon content (from 0 to 4 wt pct) and temperature (1250 °C to 1550 °C). A least-squares analysis of our data points gives an equation for the density of liquid iron-carbon alloys as a function of temperatureT [K] and carbon content [pct C] [wt pct]: ρ[g/cm3] = (7.10 - 0.0732[pct C]) - (8.28 - 0.874[pct C]) × 10-4(T - 1823) These results will give a value to within ±1.5 pct of the data of Lucas, [3] Widawski and Sauerwald, [2] and the present work.

Electrochemical Deoxidation of Titanium.

Abstract: Removal of oxygen in titanium using an electrochemical technique was examined at temperatures around 1223 K with the purpose of obtaining nearly oxygen-free titanium. Titanium and carbon electrodes, immersed in molten CaCl2, served as cathode and anode, respectively, with an external DC source. CaCl2 was employed to produce the deoxidant calcium and to facilitate the reaction by decreasing the activity of the by-product CaO. By applying about 3 V between the electrodes, the calcium potential in CaCl2 was increased at the titanium cathode surface and titanium samples of the cathode could be deoxidized by the electrolytically produced deoxidant calcium or by calcium of high activity in the CaCl2 flux. Resulting O2− species, mainly present as the deoxidation product CaO in the flux, reacted at the carbon anode to form CO (or CO2) gas which was removed from the system. Titanium wires containing 1400 mass ppm oxygen were deoxidized to less than 100 mass ppm, whereas the carbon concentration increased by about 50 mass ppm. In some cases, the oxygen concentration in titanium samples was lowered to a level less than 10 mass ppm that could be determined by conventional inert gas fusion analysis. The behavior of contaminants, such as carbon and nitrogen, is also discussed.

The effect of na and Sr modification on surface tension and volumetric shrinkage of A356 alloy and their influence on porosity formation

Abstract: Modification of the eutectic Si in Al-Si foundry alloys by adding strontium or sodium is, unfortunately, accompanied by an increase of porosity in the casting. In an attempt to understand the nature of this problem, this study used a sessile-drop method to investigate the effect of Sr and Na on surface tension and volumetric shrinkage, two probable causes of porosity occur-rence. The addition of 0.01 wt pct Sr and 0.005 wt pct Na to A356 alloy decreases the surface tension of the liquid by about 19 and 10 pct, respectively, and may increase the volume shrink-age by about 12 pct. These changes to surface tension and volumetric shrinkage promote the early formation of the pores during solidification and give the availability of a longer period of growth prior to complete solidification, resulting in a larger pore size. The effect of surface tension on the pores is more significant than volumetric shrinkage. Although the predicted pore diameter increases with lower surface tension or higher volumetric shrinkage, these two effects alone do not seem able to completely account for the observed increase in porosity that is associated with modification.

Real-time simulation of heat transfer in continuous casting

Abstract: A real-time heat-transfer model for continuous slab casting is presented. The model calculates the strand temperatures and the solid shell thickness profile along the machine as a function of the actual casting variables, strand geometry, and steel grade. The special requirements con-cerning the real-time use of the model and, in general, the accuracy of the model are also studied and discussed. The model has been tested by carrying out industrial trials. Some examples of the differences between the calculated and measured surface temperatures are presented. A spe-cial procedure to determine the boundary conditions for the secondary cooling zones from tem-perature measurements is also described.

Mechanisms of porosity formation during solidification: A theoretical analysis

Abstract: The formation of porosity during solidification is of great commercial importance and scientific interest. This is particularly so for the question of the “feeding length” of a riser. In this work, a number of theoretical models are derived and their predictions are compared to experimental observations. The comparisons show that in directional solidification, a “thermodynamic” model is useful in predicting when porosity may form. The amount of porosity predicted is too high, however, since it ignores the nucleation of the pore and growth by diffusion of dissolved gas to growing pores. A surprising conclusion of this study is that Darcy’s law does not appear to be a controlling factor in porosity distribution or formation. In particular, Darcy’s law cannot explain feeding length measurements made in steel castings. A simple “geometrical” criterion is presented instead to describe when shrinkage porosity will occur. This new model suggests a number of interesting experiments, which are proposed in discussion.

Measurement and modeling of turbulence in the gas/liquid two-phase zone during gas injection

Abstract: Averaged and turbulent fluctuating liquid velocities in the gas/liquid plume zone of a gas-stirred water model ladle were measured with a combined laser Doppler anemometer (LDA) and elec-trical probe technique. The measured turbulence fields, void fraction distribution, and gas and liquid velocities in the plume zone were used for evaluation of various turbulence models. It was found that, among all of the turbulence models tested, only a modified k-e model, with extra source terms to take into account the generation and dissipation resulting from the inter-action of the bubbles with the liquid, yielded good agreement with both the mean liquid flow field and the turbulent kinetic energy distribution. However, the values of the coefficients orig-inally proposed by their authors were found inapplicable to the bubbly plume situation; more appropriate values of the coefficients were determined based on comparison with experimental measurement.

Calculation of weld metal composition change in high-power conduction mode carbon dioxide laser-welded stainless steels

Abstract: The use of high-power density laser beam for welding of many important alloys often leads to appreciable changes in the composition and properties of the weld metal. The main difficulties in the estimation of laser-induced vaporization rates and the resulting composition changes are the determination of the vapor condensation rates and the incorporation of the effect of the welding plasma in suppressing vaporization rates. In this article, a model is presented to predict the weld metal composition change during laser welding. The velocity and temperature fields in the weld pool are simulated through numerical solution of the Navier-Stokes equation and the equation of conservation of energy. The computed temperature fields are coupled with ve-locity distribution functions of the vapor molecules and the equations of conservation of mass, momentum, and the translational kinetic energy in the gas phase for the calculation of the evap-oration and the condensation rates. Results of carefully controlled physical modeling experi-ments are utilized to include the effect of plasma on the metal vaporization rate. The predicted area of cross section and the rates of vaporization are then used to compute the resulting com-position change. The calculated vaporization rates and the weld metal composition change for the welding of high-manganese 201 stainless steels are found to be in fair agreement with the corresponding experimental results.

A mathematical model for heap leaching of one or more solid reactants from porous ore pellets

Abstract: A mathematical model is derived in dimensionless form for heap leaching of one or more solid reactants from nonreactive, porous, spherical ore particles. The model is for the interpretation of column and heap leaching data and for use in the design and scaleup of heap leaching pro-cesses. Data from experimental column leaching tests are presented which validate the model. The scope of the present study is limited to the case where the rate-controlling reagent is a component of the lixiviant solution only and not of the gas phase. The effects of particle-scale kinetic factors, heap scale and operating variables, competition between multiple solid reactants, and particle size distribution are examined using the concept of the heap effectiveness factor. It is shown that heaps operate either «homogeneously,» with distribution of reagent throughout the heap at all times, or in a «zone-wise» manner, depending mostly on a single parameter. The observed value of this parameter deviates from the predicted value in inverse proportion to the degree of contact effectiveness between the lixiviant solution and the ore particles. A rough correlation between the contact effectiveness and Reynolds number is generated from the simulation of column test results.

Inclusion behavior and heat-transfer phenomena in steelmaking tundish operations: Part II. Mathematical model for liquid steel in tundishes

Abstract: Fluid flow, heat transfer, and inclusion flotation have been modeled mathematically for several types of industrial tundish designs. Computations are presented to illustrate the importance of thermal natural convection currents in mixing the upper and lower layers of steel. The use of flow modification devices was shown to be reasonably effective in further reducing inclusion density levels at the intermediate to larger size ranges. Small inclusions (≦40 μm) were not readily removed with or without flow controls because of their low Stokes rising velocities.

Empowerment with knowledge: toward the intelligent mold for the continuous casting of steel billets

Abstract: A never-ending challenge to the competitiveness of the steel industry is the application of knowledge on the shop floor where, finally, productivity and quality are realized. The impedi-ments to the effective implementation of knowledge are largely people related and range from the level of education of the work force to entrenched attitudes of management. The develop-ment of the continuous-casting process for the production of steel billets, upon which this lecture focuses, is but one example. Looking back over 20 years, it is clear that the billet industry, in its infancy, was in a state of confusion, operating without casting standards coupled to quality, such that individual companies had developed very different practices. Research over 2 decades has established the knowledge base for the continuous casting of quality billets and set much needed standards for the design, operation, and maintenance of casting machines. The challenge now is in knowledge transfer and implementation with the aid of expert systems. Thus, the expert system for continuous casting and the concept of the intelligent billet casting mold have evolved to transcend other forms of knowledge transfer like publications and short courses. The intelligent mold effectively transfers knowledge on line to the shop floor through the combi-nation of sensors (thermocouples and load cells), signal recognition based on years of research, mathematical models of heat flow in the solidifying shell and mold, understanding of the mech-anisms of quality problems, and the formulation of a response to a given set of casting con-ditions, all controlled by an expert system. In this lecture, the drive to develop, transfer, and implement knowledge on the continuous casting of quality billets is explored. Lessons for the future are drawn from successes, failures, and frustrations in the past.

Calculation of sulfide capacities of multicomponent slags

Abstract: The Reddy-Blander model for the sulfide capacities of slags has been modified for the case of acid slags and to include A12O3 and TiO2 as components. The model has been extended to calculatea priori sulfide capacities of multicomponent slags, from a knowledge of the thermodynamic activities of the component oxides, with no adjustable parameters. Agreement with measurements is obtained within experimental uncertainty for binary, ternary, and quinary slags involving the components SiO2-Al2O3-TiO2-CaO-MgO-FeO-MnO over wide ranges of composition. The oxide activities used in the computations are calculated from a database of model parameters obtained by optimizing thermodynamic and phase equilibrium data for oxide systems. Sulfur has now been included in this database. A computing system with automatic access to this and other databases has been developed to permit the calculation of the sulfur content of slags in multicomponent slag/metal/gas/solid equilibria.

A General Model for Leaching of One or More Solid Reactants from Porous Ore Particles

Abstract: A general, unsteady-state model for leaching of one or more solid reactant species from a nonreactive, porous, spherical pellet is derived in dimensionless form for the interpretation of leaching data and for use in the design of coarse-ore leaching processes. Numerical solutions of the model equations are obtained with implicit finite difference approximations. The effects of diffusion rate, chemical reaction rate, and competition between multiple solid reactants are examined using the concept of the effectiveness factor. The importance of deposits of solid reactants on the pellet surface is ascertained. It is shown that the model is capable of simulating both “reaction-zone” and “homogeneous” kinetics, depending on the choice of parameters. The model is also capable of simulating leaching from a distribution of particle sizes, and techniques for the modification of model parameters for this purpose are discussed.

Elaboration of metal matrix composites from thixotropic alloy slurries using a new magnetohydrodynamic caster

Abstract: The working principle and the peculiarities of a new electromagnetic rheocaster, which is based on the use of rotating permanent magnets and which allows the production of intense three-dimensional (3-D) multiphase flows in solidifying semisolid alloy slurries and metal matrix composites, are described. This process can be applied to the direct continuous casting of billets, tubes, and slabs and is characterized by very low electric power consumption. Local measurement techniques are applied to the study of the evolution of non-Newtonian magnetohydrodynamic multiphase flow phenomena with the rotational speed of the inductor, the solid fraction of the aluminum alloy matrix, and the size and volume percent of SiC particles. An order of magnitude analysis of the various forces acting on the suspended crystals and SiC particles is given. The Theological behavior of electromagnetically rheocast ferrous metals, simulated by a lead-tin alloy, is also investigated. Satisfactory results concerning the microstructure of solidified aluminum slurries and aluminum matrix composites (homogeneity, crystal shape, grain size, fraction of primary solid, and distribution of SiC particles) were obtained. A discussion is presented relating the metallurgical findings to the heat and three-phase flow measurements.

Inclusion behavior and heat-transfer phenomena in steelmaking tundish operations: Part I. Aqueous modeling

Abstract: An in-house computer code, METFLO 3D, which can model three-dimensional (3-D) turbulent flow, heat transfer, and inclusion flotation, has been developed for steelmaking tundishes. Also, sensor equipment has been developed for the continuous detection of particles suspended in aqueous systems. The probe, based on the resistive pulse principle, withdraws a continuous sample of the feed water to be monitored. A full-scale (isothermal) water model tundish (Stelco Research Centre, Burlington, Canada) was used to test experimental data on particle separation within the tundish. These experimental data were compared with predictions calculated by the mathematical model developed for tundish flows, and satisfactory agreement was achieved.

Modeling of steel grade transition in continuous slab casting processes

Abstract: Mathematical models have been developed and applied to investigate the composition distributions that arise during steel grade changes in the continuous slab casting processes. Three-dimensional (3-D) turbulent flow and transient mixing phenomena in the mold and the strand were calculated under conditions corresponding to a sudden change in grade. The composition distribution in the final slab was then predicted. Reasonable agreement was obtained between predicted and experimental concentration profiles in the slab centerlines. Intermixing in the center extends many meters below the transition point, while intermixing at the surface extends above. Higher casting speed increases the extent of intermixing. Mold width, ramping of casting speed, and nozzle design have only small effects. Slab thickness, however, significantly influences the intermixing length of the slab. The axial transport of solute due to turbulent eddy motion was found to be many orders of magnitude greater than molecular diffusion and thus dominates the resulting composition distribution. Different elements, therefore, exhibited the same mixing behavior under the same casting conditions, despite having different molecular properties. Numerical diffusion caused by the finite difference schemes was investigated and confirmed to be much less important than turbulent diffusion. In the lower portion of the strand (lower than 3 m below the meniscus), the convection and diffusion can be reasonably approximated as one-dimensional (1-D) axial flow.

Kinetics of the dissolution of pure silver and silver-gold alloys in nitric acid solution

Abstract: This article describes a kinetic study of the dissolution of silver and silver-gold alloys in nitric acid. For pure Ag, the nitric acid reaction order is two at low concentrations and one for concentrations above 4 M. When attacking alloys, the reaction order is one and drops to zero when the alloy contains 51.1 pct of silver by weight or less and the nitric acid concentration is 6 M or above. The activation energy is 12.1 kcal/mol in both cases. When the molar fraction of silver is 0.70 or more, the rate of silver dissolution from its gold alloys is controlled by the chemical reaction on the solid surface. When the molar fraction of the silver is less than 0.65 and nitric acid activity and temperature are high, the dissolution is controlled by the outward diffusion of silver nitrate through the undissolved gold layer. The dissolution rate is affected by the composition of the alloy. When the molar fraction of silver is 0.76 or more, the gold atoms are found in the lattice isolated or in pairs and silver atoms may dissolve without difficulty. Between 0.55 and 0.76, the reaction rate decreases quickly when the gold content increases because the atoms make up chains into lattice and this makes the dissolution difficult. When the molar fraction is less than 0.54, the alloy does not dissolve since the gold atoms form continuous surfaces that impede the attack.

How fast can we go? The status of our knowledge of the rates of gas-liquid metal reactions

Abstract: Available information on the magnitudes of interfacial rates and the forms of rate laws is reviewed for several gas-liquid metal reactions of interest to iron and steelmaking. The relevance of some of the findings to present and proposed practical processes is briefly explored. Simple surface site blockage models provide a useful and reasonably consistent framework for the representation and analysis of the rate data, but it is found that the quantitative effects of the surface active elements, such as oxygen and sulfur, on the rates are reaction specific. Rationalization of these effects requires information on adsorption equilibria and phenomena beyond that provided by available surface tension studies

Penetration and chemical reactions in carbon cathodes during aluminum electrolysis: part i. laboratory experiments

Abstract: Penetration of metallic sodium and salt melt into cathodic carbon materials was studied in a laboratory aluminum electrolysis cell. Variables were cryolite ratio, current density, N2 or Ar atmosphere, degree of graphitization, and strain on the carbon samples. The carbon sample was analyzed by optical and electron microscopy, ash analysis, sodium detection by phenolphtalein, density, and X-ray diffraction (XRD). The developed XRD technique proved especially useful and allowed quantitative determination of concentration profiles for the crystallized compounds. Sodium was found to be the primary penetration agent and its velocity and saturation concentration increased with increased cryolite ratio of the melt and decreased graphitization of the carbon material. Sodium was found to be important as a wetting agent facilitating melt penetration. Al4C3 was not present within the pores of the carbon material. Melt penetration was enhanced by polarization and formation of nitrogen compounds. NaCN was formed directly from the elements and was destabilized by the advancing melt. In nitrogen atmosphere, A1N was the major nitrogen component and was formed within the melt phase.

Experimental investigation of dissolution rates of carbonaceous materials in liquid iron-carbon melts

Abstract: Interactions of carbonaceous materials in liquid Fe-C melts have been investigated experimentally by determining the rates of dissolution at temperatures ranging from 1623 to 1935 K. The rates of dissolution of spectroscopic graphite and an industrial coke obeyed the correlation for natural convection under turbulent conditions. The experimental data for the graphite suggested that the rate of dissolution was controlled by mass transfer in liquid boundary layer adjacent to the solid sample. The value of the empirical parameter correlating the dissolution coefficient and the operating variables was found to be 0.19, which was close to that reported in the literature. The comparison of the results obtained for coke and low-volatile coal char samples with those for the graphite revealed that impurities and porosity of the samples can effect the dissolution rates. The values ofk 1, for coke decreased with increasing the dissolution time. The examination of some of the partially dissolved coke samples by electron micro-scopy revealed that a thin, viscous ash layer was forming on the sample surface, which must be the main reason for the behavior. The dissolution rates were controlled by both mass transfer and phase boundary reactions when sulfur was present in the bath. The extent of devolatilization and dissolution of coal particles when they were injected into an Fe-C melt depended on the particle size and location.

The reduction mechanism of chromite in the presence of a silica flux

Abstract: The reduction behavior of a natural chromite from the Bushveld Complex of South Africa was studied at 1300 °C to 1500 °C Reduction was by graphite in the presence of silica Thermo-gravimetric analysis, X-ray diffraction (XRD) analysis, energy-dispersive X-ray analysis (EDAX), and metallographic analysis were the experimental techniques used Silica affected the reduction at and above 1400 °C A two-stage reduction mechanism was established The first stage, up to a reduction level of about 40 pct, is primarily confined to iron metallization, and zoning is observed in partially reduced chromites In this stage, silica does not interfere with the reduction, which proceeds by an outward diffusion of Fe2+ ions and an inward diffusion of Mg2+ and Cr2+ ions The second stage is primarily confined to chromium metallization, and formation of a silicate slag alters the reduction mechanism The slag phase agglomerates and even embeds partially reduced chromite particles An ion-exchange reaction between the re-ducible cations (Cr3+ and Fe2+) in the spinel and the dissolved cations (Al3+ and Mg2+) in the slag allows further reduction Once the reducible cations are dissolved in the slag phase, they are reduced to the metallic state at sites where there is contact with the reductant

The effects of process variables on pulsed Nd:YAG laser spot welds: Part I. AISI 409 stainless steel

Abstract: The weldabilities of AA 1100 aluminum and AISI 409 stainless steel by the pulsed Nd:YAG laser welding process have been examined experimentally and compared. The effects of Nd:YAG laser welding parameters, including laser pulse time and power intensity, and material-dependent variables, such as absorptivity and thermophysical properties, on laser spot-weld characteristics, such as weld diameter, penetration, melt area, melting ratio, porosity, and sur-face cratering, have been studied experimentally. The results of this work are reported in two parts. In Part I, the weldability of AISI 409 stainless steel by the pulse laser welding process is reported. In Part II, the weldability of A A 1100 aluminum under the same operating con-ditions is reported and compared to those of the stainless steel. When welding AISI 409 stainless steel, weld pool shapes were found to be influenced most by the power intensity of the laser beam and to a lesser extent by the pulse duration. Conduction mode welding, keyhole mode welding, and drilling were observed. Conduction mode welds were produced when power in-tensities between 0.7 and 4 GW/m2 were used. The initial transient in weld pool development occurred in the first 4 ms of the laser pulse. Following this, steady-state conditions existed and conduction mode welds with aspect ratios (depth/width) of about 0.4 were produced. Keyhole mode welds were observed at power intensities greater than 4 GW/m2. Penetration of these keyhole mode welds increased with increases in both power intensity and pulse time. The major weld defects observed in the stainless steel spot welds were cratering and large-occluded gas pores. Significant metal loss due to spatter was measured during the initial 2 ms of keyhole mode welds. With increasing power intensity, there was an increased propensity for occluded gas pores near the bottom of the keyhole mode welds.

Surface and interfacial tension of the Ni-Fe-S, Ni-Cu-S, and fayalite slag systems

Abstract: The surface tensions of the Ni-Fe-S system together with the Ni-Cu-S and fayalite-type slag systems were measured using the sessile drop technique. Drop images were obtained by X-ray radiography. For the Ni3S2-FeS pseudo-binary system, the surface tension of the matte increased with matte grade and showed a positive deviation from ideality with matte grade. This suggests that Ni3S2 dominates in the nickel matte system. The results also indicated that a fluctuation in the matte nickel content can alter the surface tension quite significantly. A ternary surface ten-sion plot of the Ni-Fe-S system showed that the addition of either Ni or S to the matte alters the surface tension. On the other hand, at a constant Ni:S ratio, the addition of iron has neg-ligible influence on the surface tension of the matte. The measured surface tension of the Ni-Cu-S system also showed a nonlinear relationship with the Cu2S content in the matte. The surface tension decreased with Cu2S content. The interfacial tension of the Ni-Fe-S and slag system was found to increase with increasing matte grade. The presence of MgO and A12O3 in the slag did not affect the interfacial tension value.

Reaction mechanism of gold dissolution with bromine

Abstract: The dissolution of gold with elemental bromine was studied by using a rotating disc technique. The main parameters studied were bromine and bromide concentrations, stirring speed, pH, and temperature. The effect of various salts, manganese, and hydrogen peroxide was also examined. The dissolution kinetics of gold with Br2 and NaBr mixture is complex. The reaction mechanism is a function of solution composition, which determines the kind of adsorbing species. For an excess concentration of bromide ions, the rate expression is Rate = (2k cl7 k al6)1/2 K 15 [Br 3 − ] and for an excess concentration of bromine, the rate expression is Rate = (2k c27 k a29)1/2 [Br−]1/2 {K25 [Br2]3/(1 +K 25 [Br2]3)}1/2 Gold in bromine solutions dissolves according to electrochemical/chemical (EC) mechanisms. The electrochemical component of the mechanism is responsible for the formation of AuBr2. In the chemical component of the mechanism, this monovalent gold bromide disproportionates into gold and stable AuBr 4 − , which reports into solution. With respect to pH, there are two characteristic dissolution regions. In the pH range of 1 to 7, gold dissolution rates were insensitive to pH. Above pH 7, gold dissolution rates decreased with increase of pH.

Deoxidation of molten titanium by electron-beam remelting technique

Abstract: The deoxidation of molten titanium was attempted by aluminum suboxide evolution in an electron-beam remelting furnace. Titanium aluminum alloy was deoxidized to about 0.05 to 0.01 wt pct oxygen in a few minutes by adding aluminum to the melt. Aluminum activity in the alloy was estimated by the evaporation rate of aluminum.

Calculation of dendrite settling velocities using a porous envelope

Abstract: The convective transport and gravitational settling of unattached equiaxed grains and dendrite fragments can cause macrosegregation and influence the structure of the equiaxed zone in a variety of solidification arrangements. An understanding of how the highly nonspherical geometry of the dendrite influences its settling and transport characteristics is needed to determine the motion of unattached dendrites and predict structure and segregation in castings. The empirical results of previous works have been used to develop a FORTRAN 77 computer program to calculate the settling velocity of various dendritic shapes and a number of other parameters of interest, such as the volume and surface area of the dendrite. Required inputs to the code are the physical properties of the system and some simple geometric parameters of the dendrite being considered, such as the average radius of the primary arm. The predicted settling velocities were on average within ±5 pct of those measured for model dendrites and were consistent and in good agreement with three other experimental investigations. Future development of the code will attempt to overcome many of its present limitations by including particle-particle interactions and the effects of tertiary arms, for example.

Thermodynamics of iron-aluminum alloys at 1573 K

Abstract: The activities of iron and aluminum were measured in Fe-Al alloys at 1573 K, using the ion-current-ratio technique in a high-temperature Knudsen cell mass spectrometer. The Fe-Al solutions exhibited negative deviations from ideality over the entire composition range. The activity coefficients gamma(Fe), and gamma(Al) are given by six following equations as a function of mole fraction, X(Fe), X(Al). The results show good agreement with those obtained from previous investigations at other temperatures by extrapolation of the activity data to 1573 K.

How are new orientations generated during primary recrystallization

Abstract: High-voltage electron microscopy (HVEM) of in situ recrystallizing single crystals and growth competition experiments, according to Beck, have been performed in order to better understand how new orientations develop during primary recrystallization. The specimens used were single crystals of Al, Cu, Cu with Mn, or P additions in order to vary stacking fault energy and size misfit of the solute. Evidently, nucleation is always in orientations of the deformed matrix. New orientations develop by annealing twinning, unless the deformation microstructure (DM) of a rolled polycrystal is already inhomogeneous enough. In both cases, the same fast-growing grain boundaries (GBs) determine the final recrystallization texture. These GBs differ depending on purity and solute and can be characterized (and compared with respect to calculated structures) by the nearest coincidence site density [Sigma][sup [minus]1].

Gaseous reduction of laterite ores

Abstract: Lateritic nickel ores have been reduced under laboratory conditions. The reduction experiments were carried out at temperatures from 500 °C to 1100 °C in a horizontal tube furnace using various mixtures of H2 and CO2. The hydrogen evolution method was used to measure the degree of metallization of the reduced ore. It was found that the rate of reduction was very low at 500 °C but then increased rapidly upon heating the ore to 600 °C. The percent metallics increased with increasing H2 to CO2 ratios in the reducing gas. At temperatures between 600 °C and 1100 °C, a H2 to CO2 ratio of 3 leads to the formation of 5 to 6 pct metallics in the reduced calcine was shown. Heating the ore in air or nitrogen prior to reduction does not affect the degree of metallization. A H2 to CO2 ratio of at least 4 is required to obtain a ferronickel product analyzing 36 pct nickel if no further reduction is carried out during the subsequent smelting operation.

Thermodynamics of oxygen and nitrogen in liquid iron equilibrated with CaO- SiO2-Al2O3 slags

Abstract: Nitrogen distribution ratios, LN ( = (mass pct N)/[mass pct N]), between CaO-SiO2-Al2O3 slags and liquid iron were measured at 1823 and 1873 K as a function of Si (or Al) content in metal, using lime and alumina crucibles. Based on these results and the reported values for activities of SiO2 (or Al2O3), nitride capacities, C(N), defined by (mass pct N) · PO2/3/4/PN2/1/2 were evaluated. Activities of SiO2 (or Al2O3) obtained by using the values for LN and C(N) obtained in present and previous gas-slag experiments were compared with previous results.