Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1971"

Mechanism of bond zone wave formation in explosion-clad metals

Abstract: Results of experiments in which the collision variables were carefully controlled showed that bond zone wave formation during explosion cladding is analogous to the formation of vortex streets in fluid flow around an obstacle or in the collision of liquid streams. The fluid flow analogy explains the observed transition from a smooth metal-to-metal bond zone to a wavy bond zone above a critical collision velocity. This model is capable of predicting the minimum collision velocity necessary for bond zone wave formation in different metal systems and it also predicts correctly the strong dependence of wave size on collision angle. The magnitude of the wave size agrees with that predicted from fluid flow past a flat plate. Two other mechanisms of bond zone wave formation were explored experimentally and found to be invalid.

Gaseous reduction of iron oxides: Part I. Reduction of hematite in hydrogen

Abstract: The reduction of high-grade hematite ore in hydrogen has been investigated. There is an unusual temperature effect for small granules with a dip in the rate at about 700°C, similar to those reported by previous investigators for different types of iron oxides. The particlesize effect on the time of reduction suggests that there are three major limiting rate-controlling processes: i) uniform internal reduction, ii) limiting mixed control and iii) gas diffusion in porous iron layer. Processes (ii) and (iii) are special cases of a so-called topochemical mode of reduction associated with the formation of product layers. Unidirectional reduction experiments revealed the significant role played by gas diffusion in porous iron layer as a rate-controlling process. The effective H2-H2O diffusivity in porous iron derived from, the reduction data is found to decrease markedly with decreasing reduction temperature. This is consistent with the fracture surfaces of porous iron as viewed by scanning electron microscopy. The present interpretation of the rate of reduction of hematite ore is found to apply equally well to previously published data on the hydrogen-reduction of natural and synthetic hematite pellets.

Thermodynamics of the Fcc Fe−Ni−C and Ni−C alloys

Abstract: The activity of carbon in the fcc solid solution of the Fe−Ni−C system has been measured at 800°, 1000°, and 1200°C by comparison with observed values in the Fe−C binary by equilibration with methane-hydrogen mixtures. Defining the lattice ratioz C≡n C/(n Fe+n Ni−n C), the activity coefficient ΨC≡a C/z C has been determined as a function of temperature and composition. At infinite dilution log ΨC goes through a maximum at about 70 pct Ni in agreement with Smith. The partial molar free energy of carbon in the dilute solution referred to graphite is not a linear function of the base alloy composition, but has a large deviation with maximum at about 60 pct Ni. Similar maxima occur in both ΔH C ° and ΔS C ° . Linear equations are derived for the activity coefficient of carbon in three composition ranges of Fe−Ni−C alloys; a simplified equation applicable to nickel steels is included. The solubility of graphite in nickel has been determined. The marked deviation from linearity is ascribed to the existence of iron atoms in two electronic states, γ1 and γ2 which differ in energy and are antiferromagnetic and ferromagnetic, respectively.

The formation of Hcp and Bcc phases in austenitic iron alloys

Abstract: The formation of the hcp (∈) and bcc (α) structures in pure iron under high pressure conditions, as well as the morphological and crystallographic aspects of martensitic transformation to these structures at atmospheric pressure in iron alloys, are reviewed., It is concluded that the unique features of α- or lath martensite formation are not dependent upon the presence of the ∈ phase. Application of the phenomenological theory of martensitic transformation has not successfully rationalized the crystallography of lath-martensite. The criterion for ∈- and α-phase formation is established using the regular solution approximation and appropriate lattice stability parameters. In particular, the ∈ phase can be formed in Fe−Ni−Cr compositions through stress-induced transformation attending α-martensite formation. Further consideration suggests that the ∈→α transformation is not expected at atmospheric pressure at temperatures below approximately 500°K in the alloys considered. Thus, two martensitic transformations, γ→∈ and γ→α, can occur jointly in certain alloys.

The growth of lamellar eutectic structures in the Pb−Sn and Al−CuAl2 systems

Abstract: Results of an investigation into the variation in lamellar spacing with composition are presented, together with measurements of diffusion coefficients in the Pb−Sn and Al−CuAl2 systems. These results are used to investigate the validity of eutectic growth theory. It is concluded that the basic theory can explain the growth of Pb−Sn, but not that of the Al−CuAl2 system. It is suggested that the neglect of kinetic undercooling terms is responsible for the discrepancy with the Al−CuAl2 system.

Some recent results on magnetism in alloys

Abstract: The effect of local atomic environment on the atomic moment of Fe in Fe−Al alloys and of V in Au−V alloys is reevaluated, using improved methods of analysis and new magnetic data. Magnetic clusters with giant moments occur in many alloys in which one of the components has no magnetic moment. This is true for FeAl in spite of the presence of well-developed atomic long range order, although the concentration of magnetic clusters does decrease with increasing long range order. The phenomena of mictomagnetism are reviewed. Mictomagnetism occurs in many alloys having no long range atomic order, and it is characterized by the freezing of the spin orientations at low temperatures but, in contrast to ferromagnetism and to antiferromagnetism, without long range magnetic order.

Silicide precipitation in the Ti−Zr−Al−Si system

Abstract: Silicide precipitation has been studied in a number of martensitic Ti−Si alloys and ternary and more complex alloys containing zirconium and aluminum. The precipitation has been shown to be strongly influenced by composition. Heterogeneous nucleation of Ti5Si3 occurs at, and above, 500°C in binary Ti−Si alloys containing up to 2.4 pct Si and little conventional precipitation hardening can be achieved. Zirconium additions are incorporated into the silicide and produces finer, more stable particle dispersions accompanied by an improved aging response. If critical concentrations of zirconium (approximately 5 pct) and silicon (approximately 1 pct) are present, matrix nucleation of G.P. zones occurs at, and below 550°C. This is accompanied by a significant aging response. Additions of aluminum reduce the rate of precipitate growth while having little effect on the nature of the precipitates produced. It has been shown that typical commercial heat treatments of “near α” silicon-bearing alloys (0.5 pct Si max) do not produce silicide dispersions.

On the toughness increment associated with the austenite to martensite phase transformation in TRIP steels

Abstract: The fracture toughness of a high carbon TRIP alloy, deformed approximately 75 pct at 460°C was investigated over a range of temperatures from −196°C to 200°C. Two distinct temperature regimes were present: a low temperature regime where martensite formed during fracturing and a high temperature regime where no martensite formed. The toughness values of the low temperature regime were higher than the extrapolated values of the high temperature regime indicating that the transformation makes a positive contribution to the fracture toughness of TRIP alloys. For the alloys used in this investigation the room temperature plane strain fracture toughnessK IC was on the order of 95 ksi\(\sqrt {in} \) or in terms of the crack extension forceG IC, 274 in.-lb per sq in. The fracture mode was cleavage and the extraordinary toughness for this mode of crack extension is attributed to the energy absorbed by the simultaneous phase transformation. The contribution due to the phase transformation was determined to be in the range 37 to 57\(\sqrt {in} \) in terms of stress intensity or 168 to 232 in.-lb. per sq in. in terms of crack extension force using the extrapolation technique. The results obtained using the extrapolation technique represent the first experimental determination of the toughness contribution associated with the austenite to martensite phase transformation in TRIP alloys. An expression for the toughness associated with the transformation was derived using fundamental fracture mechanics relations. This expression, which contains easily measured parameters, was used to calculate the toughness contribution due to the phase transformation and the results were in good agreement with the experimental values.

Martensite and retained austenite in hot-rolled, low-carbon bainitic steels

Abstract: The microstructure and occurrence of a microconstituent, consisting of martensite and retained austenite in hot-rolled plates of low-carbon bainitic steels was studied by electron microscopy and microprobe analysis. The results of the studies showed that the formation of the martensite-austenite constituent is controlled by the composition of the steel and by the cooling rate of the plates following hot-rolling. The mechanisms involved in the formation of the martensiteaustenite constituent are discussed.

Mechanism and kinetics of bubble formation in doped tungsten

Abstract: The mechanisms and kinetics of bubble formation that occur during annealing of tungsten doped with small amounts of K, Al, and Si compounds has been investigated by electron microscopy. Bubbles are present in the sintered ingot due to volatilization of the dope during the sintering treatment. As the ingot is worked down into wire, the bubbles present in the ingot become elongated. On annealing these elongated bubbles undergo shape changes which depend on the amount of working. Elongated bubbles with a length-to-width ratio of less than ten spheroidized while those with a length-to-width ratio greater than twenty are unstable and break up into a row of bubbles. If working has been sufficient to close up the elongated bubbles,e.g., in ribbon, 0.125 mm thick rolled from 0.9 mm diam wire, bubble formation results from the diffusion of vacancies to the volatile dopant particles.

The effects of applied stress on the martensitic transformation in TiNi

Abstract: The deformation behavior of TiNi at 20°C has been investigated as a function of composition and of the prior heat treatment. Wide mechanical property variation and significant differences between the effects of tensile and of compressive loading were observed. Under some conditions anelastic behavior, characterized by a broad hysteresis loop, was reproducibly obtained. The effects of heating the deformed materials aboveA f on the subsequent stress-strain behavior indicate the anomalies observed to be directly related to the martensitic transformation. The effects of stress application on the martensitic transformation are discussed. It is shown that, under some conditions, the stress-assisted transformation structures may be unstable on the removal of the stress. At test temperatures outside theM f toA f range, this can result in anelastic behavior. More complex behavior expected at temperaturesM f < T < Af, is discussed in some detail. It is shown that both the anelastic behavior and the “shape memory” can be accounted for by the effects of applied stress. It is also shown that the mechanical properties in this temperature range can vary markedly with the prior heat treatment, even at temperatures not normally considered of significance. Though based on observations made on TiNi, the phenomena discussed are inherent in materials undergoing a martensitic transformation over a narrow range of temperatures.

Gaseous reduction of iron oxides: Part II. Pore characteristics of iron reduced from hematite in hydrogen

Abstract: The pore structure of iron reduced from hematite ore by hydrogen is charactertized from measurements of pore volume, pore area and effective gas diffusivity. The measured connected pore volume within the range 0.22 to 0.34 cu cm per g is about the same as the total pore volume; that is, most of the pores in the reduced iron are interconnected. The pore area measured by the BET technique increases with decreasing reduction temperature,e.g. from 0.1 sq m per g at 1200°C to 39 sq m per g at 200°C. The effective H2−H2O diffusivity, measured directly at 600°C after reduction of the ore in hydrogen at the same temperature, is in excellent agreement with that derived from the reduction data. The pore-diffusivity measurements were also made at room temperature using iron samples reduced in hydrogen at 800° and 1000°C. On the basis of the pore properties measured, it appears that the reduced iron has a regular pore structure which becomes finer with decreasing reduction temperature. The effective diffusivities computed on the basis of a simple pore structure are found to be in accord with those derived previously from the reduction data.

The strength and fracture toughness of 18 Ni (350) maraging steel

Abstract: The influence of microstructure on the strength and fracture toughness of 18 Ni (350) maraging steel was examined. Changes in microstructure were followed by X-ray and neutron diffraction and by optical and electron microscopy. These observations have been correlated with the fracture morphology established by scanning electron microscopy. Air cooling this alloy from the austenitizing temperature results in a dislocated martensite. During the initial stage of age hardening, molybdenum atoms tend to cluster (forming preprecipitates) and the cobalt assumes short range ordered positions. Subsequent aging results in Ni3Mo and σ-FeTi with overaging being associated with the formation of equilibrium reverted austenite and Fe2Mo. The fracture behavior is examined in terms of elementary dislocation precipitate interactions. It is suggested that the development of coplanar slip in the underaged conditions leads to its increased stress corrosion susceptibility and decreased fracture toughness. The optimum aged condition is then associated with cross-slip deformation. The fracture behavior of the overaged condition is a dynamic balance between a brittle matrix and the ductile (crack blunting) reverted austenite.

The effect of particle size distribution on the performance of a phosphate flotation process

Abstract: A 25 cu ft flotation cell was operated continuously to produce an apatite-rich concentrate. The experimental results reported in this paper attempt to elucidate the role of the particle size distribution upon the performance of the cell. The particle size distribution influences performance through its effect on the particle residence time distribution and on the rate of impaction, adherence and detachment of particles and bubbles. A model is developed which is capable of predicting a fractional recovery of apatite in any particular particle size range.

Order-strengthening in Cu−Al alloys

Abstract: Cu−Al alloys can be significantly strengthened after deformation by a suitable low temperature thermal treatment. Possible mechanisms for this strength increase have been investigated using a number of techniques including differential thermal analysis, electron microscopy and diffraction. It has been found that strength increases could be associated with the development of order in the alloys, and the magnitude of the increases have been found to be dependent on the amount of prior deformation, the amount of order and thee/a ratio. An ordered phase based on an fcc lattice has been identified at higher aluminum concentrations. It is suggested that this phase is Cu3Al. It is postulated that strain fields associated with the formation of ordered regions which nucleate on stacking faults are responsible for the observed strengthening.

The surface tensions of Pb, Sn, and Pb-Sn alloys

Abstract: The surface tensions of 99.9999 pct Pb and Sn and of alloys made from lead and tin of the same purity have been measured by the sessile-drop method. The surface tension of lead was determined from the melting point, the surface tension of tin from 200°C (32°C of supercooling) and the surface tensions of the Pb−Sn alloys from the respective liquidus temperatures, all, up to a temperature of about 560°C. Within the limits of experimental error, data for both pure metals plot in a rectilinear fashion with negative slopes, thus: γlead=472.7−0.085t(±5) dyne/cm γtin=569.0−0.080t((±5) dyne/cm The surface tensions of Pb−Sn alloys are not straight-line functions of temperature and the evidence indicates that the temperature coefficients of surface tension are slightly positive at the liquidus temperature.

Carbides in M-50 high speed steel

Abstract: The carbides in M-50 high speed tool steel were studied in detail. The dissolution of carbides as a function of austenitizing temperature, and their precipitation as a function of tempering temperature were characterized by X-ray diffraction and microchemical analysis. The carbides in the annealed steel are M23C6, M6C, M2C, and MC. Upon austenitizing, with increasing temperatures, the carbides dissolve in the order: M23C6, metastable M2C, M6C, and MC. The residual carbides in the heat treated steel are MC and stable M2C. The solvus temperatures of M23C6 and M6C were determined. Upon tempering the hardened steel, with increasing tempering temperatures, carbides precipitate in the order: M23C6, metastable M2C, MC, and M6C. It is shown that the composition of the precipitated metastable M2C is different from that of the residual stable M2C and it varies with the tempering temperature.

Yield surfaces in prestrained aluminum and copper

Abstract: The analysis of strain-hardening materials subjected to multiaxial states of stress requires more detailed experimental information about the effects of previous plastic deformation on the yield surfaces of real materials than is presently available. To provide insight into some of these effects thin walled tubular specimens of 1100-0 aluminum and annealed OFHC copper were subjected to biaxial stresses through the application of simultaneous axial tension and internal pressure, and the effects of the magnitude, direction, and sequence of prestraining operations on subsequent yield surfaces were determined. It was found that the yield surface behavior depends greatly upon the definition of yielding employed. Use of small proof strain definitions resulted in very anisotropic yield surface characteristics which reflected the effect of previous deformation. On the other hand, use of large proof strains resulted in isotropic yield surface characteristics which were devoid of previous deformation influence. The small proof strain yield curves were found, in general, to expand and translate in the direction of prestrain and, for biaxial prestrains, to be distorted in the vicinity of the loading point. Multiple prestrain sequences in normal directions induce a large negative cross effect similar to Bauschinger effect observed under reversed loading. Such anisotropic behavior was found to contradict the two most commonly used continuum mechanics predictions, the isotropic and kinematic hardening rules.

Fracture and fractography of metastable austenites

Abstract: External test variables such as rate and temperature, and changes in alloy composition are shown to have a number of effects on the fracture of high-strength, metastable austenitic steels. One rate-dependent phenomenon is an unusual fracture mode transition wherein a flat mode changes to a shear mode when the amount of transformation product in the vicinity of the crack tip is reduced by adiabatic heating. The point at which this happens in any one test is dependent upon the velocity of the slowly growing crack which in turn is dependent upon the crosshead rate. Because of this rate effect, the plane stress fracture toughness decreases by as much as 30 pct at higher crosshead rates. Fractographically, it was ascertained that at room temperature, both phases failed in a ductile manner, but at −196°C, martensite containing greater than about 0.27 wt pct C would cleave. This resulted in a “ductile-brittle” transition in metastable austenites at −196°C as a function of carbon content. Other compositional variations change the austenite stability which controls the amount of strain-induced marteniste occurring at the crack tip. It is shown that a plane stress fracture toughness (KC) approaching 500,000 psi-in.1/2 may be achieved by decreasing the stability of the austenite. The variation ofKc with austenite stability agrees qualitatively with a theoretical model for the invariant shear contribution to the fracture toughness of metastable austenites.

Prediction of activation energies for creep and self-diffusion from hot hardness data.

Abstract: It is shown that the activation energy for creep or self-diffusion for pure metals can be determined from hot hardness data above 0.75T m by means of the expressionH/E=G expQ L/nRT· HereH is the hot hardness,E is the elastic modulus,G is a material constant,Q L is the lattice self-diffusion activation energy,R is the gas constant,T is the absolute temperature, andn is the stress exponent for creep assumed equal to five. Hot hardness data above 0.5T m plotted as logarithmH/E against reciprocal absolute temperature reveal two straight lines with a break observed at about 0.75T m. It is shown that the break occurs at a value of strain rate, ∈, over lattice self-diffusivity,D L, of about 109, a value associated with power-law breakdown for creep. These observations suggest two conclusions regarding the rate-controlling process during hot indentation testing of pure metals. Between 0.75 and 1.0T m, the deformation process is associated with lattice self-diffusion and creep flow in the power. law region. Between 0.5 and 0.75T m the rate-determining process is associated with dislocation pipe diffusion and creep flow in the power-law breakdown region.

Heat treatment of 706 alloy for optimum 1200 °F stress-rupture properties

Abstract: Evaluation of a commercial heat treatment for 706 alloy indicated that it resulted in relatively low 1200° F stress rupture ductility. It was determined that this was caused by a solution treatment which dissolved all of the age-hardening phases in the alloy and caused a coarse grain size and supersaturated matrix condition. Based upon extensive fine structure study of the 706 alloy as well as previous experience with 718 alloy and other Fe−Ni-base superalloys, a heat treatment is developed which effectively optimizes the 1200°F stress-rupture properties of the alloy. The key to best properties was found to be the precipitation of globular to plate-like Ni3Cb/Ni3Ti at the grain boundaries in conjunction with maintaining a fine as-forged grain structure.

Strain instability and fracture at the surface of upset cylinders

Abstract: A refined method has been developed for measurement of the localized surface strains during axial compression of cylinders. The method has been applied to 1045 steel cylinders in various conditions to study fracture under combined stress states. Because the refined measurement method is used, perturbations are observed in the strain path which would otherwise not be apparent. These perturbations precede surface fracture in every case. It is shown that geometric similarities exist between the strain perturbations in upsetting and those in trough formation preceding fracture in stretch forming of sheet material. In addition, metallographic examination of transverse sections of the upset cylinders reveals the presence of subsurface void formations prior to fracture. It is concluded that the surface fractures in upset cylinders involve localized necking of material between inhomogeneities, and it is suggested that an accurate model of this behavior may give some understanding of the influence of material parameters on fracture.

Fatigue crack propagation in copper and Cu-Al single crystals

Abstract: The effect of crystallographic orientation, temperature, and stacking fault energy on the rate of fatigue crack propagation was studied in polycrystalline copper, copper single crystals, and Cu−Al single crystals at room temperature and at liquid nitrogen temperature. A stress intensity factor was used to normalize the crack propagation data. It was found that dislocation cross slip plays a critical role on the rate of fatigue crack propagation. Existing mathematical crack propagation formulae could not explain the data on single crystals. A new fatigue crack propagation model to explain the observed results is proposed.

Precipitation in the system Al-0.05 wt pct Fe

Abstract: The precipitation reaction in an aluminum alloy containing 0.05 wt pct Fe (enriched in Fe57) was studied using Mossbauer spectroscopy. It was found that in addition to the equilibrium precipitate, Fe Al3, the metastable phase FeAl6 occurs as well. Formation of FeAl6 is favored when the rate of precipitation is accelerated by cold working the supersaturated alloy. Step anneal experiments were performed in an effort to determine an activation energy for growth of precipitate particles. The results of these experiments are not entirely consistent with simple models of the nucleation and growth process.

Crystallography of the martensite transformation in Fe−Al−C alloys

Abstract: Crystallographic measurements on highly tetragonal bct martensite in two Fe−Al−C steels have been made and the results have been interpreted in terms of the phenomenological crystallographic theory of martensite formation. Agreement between theory and experiment was found to be excellent. Of particular interest is the high martensite tetragonality (c/a→1.14) in aluminum-steels compared to others. Because of this the principal distortions of the Bain deformation are substantially smaller and consequently the magnitudes of the shape and lattice invariant deformations are reduced considerably. Measurements of the dilatation parameter δ indicate that the shape deformation is not significantly different from an invariant plane strain.

The effect of frequency on the cyclic strain and low cycle fatigue behavior of cast Udimet 500 at elevated temperature

Abstract: An experimental investigation was undertaken on cast Udimet 500 to study principally the effect of frequency on low cycle fatigue at temperatures from 730° to 900°C, but mostly at 815°C (1500°F). Total strain range and stress range vs fatigue life relationships were determined which included the frequency following the form of author's recent work. The stress range was found to obey a power law relationship involving the fatigue life and frequency, such that at a specific stress range, a ten-fold decrease in frequency corresponded to a 3.7-fold decrease in life. While stress results were well-ordered with frequency, the scatter in the cyclic strain data was severe. A random crystallographic orientation of the few grains in the cross-section led to an anisotropy in the material which produced as much as a three-fold variation in diametral strain around the circumference.

The morphology and substructure of highly tetragonal martensites in Fe-7 pct Al−C steels

Abstract: This investigation reports on an optical and electron microscope study of bct martensite formed in Fe-7 pct Al-1.5 pct C and Fe-7 pct Al-2.0 pct C alloys. In each case the martensite is plate-like containing\((112)[\bar 1\bar 11]\) transformation twins 100 to 200A in width. The particular twin plane variant\((112)[\bar 1\bar 11]\) corresponds to the martensite habit plane variant (3, 15, 10)F, which is predicted by the crystallography theory. The twins are uniformly spaced and extend completely from one martensite-austenite interface to the other as would be theoretically expected. The martensite plates are ideally lenticular in the 2 pct C alloy but those in the 1.5 pct C alloy frequently exhibit irregular interfaces which are attributed to impingement effects. All observations are in accordance with the phenomenological crystallography theory as applied to ferrous martensites with a {3, 15, 10}F habit plane.

Kinetics of zinc oxide reduction with carbon monoxide

Abstract: Reduction of ZnO single particles with CO was investigated at atmospheric pressure from 1000° to 1500°C. Weight loss data up to about 90 pct reduction were easily reproducible for the dense photoconductive grade ZnO particles but not for the American grade samples, whose scatter was attributed to the 13 pct residual internal porosity and to impurities. The data agreed closely with a mixed regime model, which pictures external diffusion acting in series with an irreversible first order kinetic process at the surface. After the diffusional contribution was subtracted, activation energies of 37,900 (±2040) cal per mole and 20,600 (±10,200) cal per mole were obtained for the photoconductive and American grades, respectively. For the photoconductive grade the mixed regime model gave a good fit over the entire temperature range. Diffusional limitations were approached at 1500°C.

The surface tension of liquid silver alloys: Part II. Ag−O alloys

Abstract: The surface tensions of liquid Ag-O alloys have been determined by the sessile drop method. The surface activity of oxygen, as measured by −(dσ/dX O)XO→0j, where σ is the surface tension of the metal andX O the mole fraction of oxygen, is quite large and equals 3.80×105 dyne per cm at 980°C and 1.35×105 dyne per cm at 1108°C. The heat of adsorption of oxygen is estimated to be of the order of 30 kcal per mole. Application of the monolayer approximation shows that liquid silver becomes saturated with oxygen when each adsorbed oxygen atom occupies an area of 33±5A2. Small additions of platinum to silver do not change the characteristics of the adsorption of oxygen appreciably. An analysis of the data is consistent with the conclusion that saturation of the surface of liquid silver with oxygen results from the formation of an ionic two-dimensional compound at the surface. This hypothesis is tested in the case of several other systems and yields satisfactory results. The structure of these compounds is discussed. In the case of the Ag-O system, it appears to correspond to the stoichiometry Ag3O.

Diffusion of managenese and silicon in liquid iron over the whole range of composition

Abstract: The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al2O3). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D Fe−Mn=1.8×10−3 exp (−13,000/RT) cm2/sec The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)2}×10−5 cm2/sec The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at various concentrations is as follows:D Fe−Si=2.8×10−3 exp (−11,900/RT) cm2/sec at 20 pct SiD Fe−Si=2.1×10−3 exp (−13,200/RT) cm2/sec at 12.5 pct SiD Fe−Si=5.1×10−4 exp (−9,150/RT) cm2/sec at 2.2 pct Si